Update documentation

Author: otherguy

README.md

@@ -1,4 +1,4 @@
-# 💱 PHP Currency API
+# 💱 PHP Currency Exchange Rate API
 _A PHP 7 API Wrapper for Popular Currency Rate APIs._
 
 [![Version](https://img.shields.io/packagist/v/otherguy/php-currency-api.svg?style=flat-square)](https://packagist.org/packages/otherguy/php-currency-api)
@@ -11,19 +11,17 @@ _A PHP 7 API Wrapper for Popular Currency Rate APIs._
 Dont worry about your favorite currency conversion service suddenly shutting down or switching plans on you. Switch away easily.
 
 ## Inspiration 💅
-
-I needed a currency conversion API for [my travel website]() but couldn't find a good PHP package. The idea of the
+I needed a currency conversion API for [my travel website]() but could not find a good PHP package. The idea of the
 [`Rackbeat/php-currency-api`](https://github.com/Rackbeat/php-currency-api) package came closest but unfortunately it
 was just a stub and not implemented.
 
 ## Features 🌈
-
 * Support for [multiple different APIs](#supported-apis-) through the use of drivers
-* Consistent return interface, independent of the driver being used
+* A [fluent interface](#fluent-interface) to make retrieving exchange rates convenient and fast
+* Consistent return interface that is independent of the driver being used
 * [Calculations](#conversion-result) can be made based on the returned data
 
 ## Supported APIs 🌐
-
 | Service                                              | Identifier          |
 |------------------------------------------------------|---------------------|
 | [FixerIO](https://fixer.io)                          | `fixerio`           |
@@ -35,13 +33,11 @@ was just a stub and not implemented.
 _If you want to see more services added, feel free to [open an issue](https://github.com/otherguy/php-currency-api/issues)!_
 
 ## Prerequisites 📚
-
 * `PHP 7.1` or higher (Tested on: PHP `7.1` ✅, `7.2` ✅ and `7.3` ✅)
 * The [`composer`](https://getcomposer.org) dependency manager for PHP
 * An account with one or more of the [API providers](#supported-apis-) listed above
 
 ## Installation 🚀
-
 Simply require the package using `composer` and you're good to go!
 
 ```bash
@@ -51,10 +47,11 @@ $ composer require otherguy/php-currency-api
 ## Usage 🛠
 
 ### Currency Symbol Helper
-
 The [`Otherguy\Currency\Symbol`](src/Symbol.php) class provides constants for each supported currency. This is merely
 a helper and does not need to be used. You can simply pass strings like `'USD', 'EUR', ...` to most methods.
 
+> Please note that you are not required to use `Otherguy\Currency\Symbol` to specify symbols. It's simply a convenience helper.
+
 ```php
 // 'USD'
 $symbol = Otherguy\Currency\Symbol::USD;
@@ -82,7 +79,6 @@ $symbols = Otherguy\Currency\Symbol::name( Otherguy\Currency\Symbol::USD );
 ```
 
 ### Initialize API Instance
-
 ```php
 $currency = Otherguy\Currency\DriverFactory::make('fixerio'); // driver identifier from supported drivers.
 ```
@@ -94,11 +90,26 @@ To get a list of supported drivers, use the `getDrivers()` method:
 $drivers = Otherguy\Currency\DriverFactory::getDrivers()
 ```
 
-### Set Base Currency
+### Set Access Key
+Most API providers require you to sign up and use your issued access key to authenticate against their API. You can
+specify your access key like so:
+
+```php
+$currency->accessKey('your-access-token-goes-here');
+```
+
+### Set Configuration Options
+To set further configuration options, you can use the `config()` method. An example is
+[CurrencyLayer's JSON formatting option](https://currencylayer.com/documentation#format).
+
+```php
+$currency->config('format', '1');
+```
 
+### Set Base Currency
 You can use either `from()` or `source()` to set the base currency. The methods are identical.
 
->**Note:** Each driver sets its own default base currency. [FixerIO](https://fixer.io) uses `EUR` as base currency
+> **Note:** Each driver sets its own default base currency. [FixerIO](https://fixer.io) uses `EUR` as base currency
 > while [CurrencyLayer](https://currencylayer.com) uses `USD`.
 
 Most services only allow you to change the base currency in their paid plans. The driver will throw a 
@@ -110,38 +121,52 @@ $currency->from(Otherguy\Currency\Symbol::USD);
 ```
 
 ### Set Return Currencies
+You can use either `to()` or `symbols()` to set the return currencies. The methods are identical. Pass a single currency
+or an array of currency symbols to either of these methods. 
 
-You can use either `to()` or `symbols()` to set the return currencies. The methods are identical.
-
+> **Note:** Pass an empty array to return all currency symbols supported by this driver. This is the default if you
+> don't call the method at all. 
+ 
 ```php
-$api->to([ Otherguy\Currency\Symbol::BTC, Otherguy\Currency\Symbol::EUR, Otherguy\Currency\Symbol::USD ]);
+$currency->to(Otherguy\Currency\Symbol::BTC);
+$currency->symbols([Otherguy\Currency\Symbol::BTC, Otherguy\Currency\Symbol::EUR, Otherguy\Currency\Symbol::USD]);
 ```
 
-*Please note, you are not required to use `Otherguy\Currency\Symbol` to specify symbols. It's simply a convenience helper.*
-
-### Get latest rates
+### Latest Rates
+This retrieves the most recent exchange rates and returns a [`ConversionResult`](#conversion-result) object.
 
 ```php
-$api->get(); // Get latest rates for selected symbols, using set base currency
-$api->get('DKK');  // Get latest rates for selected symbols, using DKK as base currency
+$currency->get(); // Get latest rates for selected symbols, using set base currency
+$currency->get('DKK');  // Get latest rates for selected symbols, using DKK as base currency
 ```
 
-### Convert amount from one currency to another
+### Historical Rates
+To retrieve historical exchange rates, use the `historical()` method. Note that you need to specify a date either as a
+method parameter or by using the `date()` methods. See [Fluent Interface](#fluent-interface) for more information.
 
 ```php
-$api->convert($fromCurrency = 'DKK', $toCurrency = 'EUR', 10.00); // Convert 10 DKK to EUR
+$currency->date('2010-01-01')->historical();
+$currency->historical('2018-07-01');
 ```
 
-### Get rate on specific date
+### Convert Amount
+Use the `convert()` method to convert amounts between currencies.
+
+> **Note:** Most API providers don't allow access to this method using your free account. You can still use the 
+> [Latest Rates](#latest-rates) or [Historical Rates](#historical-rates) endpoints and perform calculations or conversions
+> on the [`ConversionResult`](#conversion-result) object.
 
 ```php
-$api->historical($date = '2018-01-01'); // Get currency rate for base on 1st of January 2018
-$api->historical($date = '2018-01-01', 'GBP'); // Get currency rate for GBP on 1st of January 2018
+$currency->convert(10.00, 'USD', 'THB'); // Convert 10 USD to THB
+$currency->convert(122.50, 'NPR', 'EUR', '2019-01-01'); // Convert 122.50 NPR to EUR using the rates from January 1st, 2019
 ```
 
+### Fluent Interface
+`TODO`
+
 ### Conversion Result
+`TODO`
 
 ## Contributing 🚧
-
 [Pull Requests](https://github.com/otherguy/php-currency-api/pulls) are more than welcome! I'm striving for 100% test 
 coverage for this repository so please make sure to add tests for your code. 

src/Drivers/CurrencyLayer.php

@@ -20,7 +20,7 @@ class CurrencyLayer extends BaseCurrencyDriver implements CurrencyDriverContract
   protected $baseCurrency = Symbol::USD;
 
   protected $httpParams = [
-    'format' => 1,
+    'format' => 0,
   ];
 
   /**