feat: added helper functions for measurement system units

Author: andrepimpao

src/MeasurementSystem/Fahrenheit.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace ProgrammatorDev\OpenWeatherMap\MeasurementSystem;
+
+class Fahrenheit
+{
+    public const ATMOSPHERIC_PRESSURE_UNIT = 'hPa';
+    public const CLOUDINESS_UNIT = '%';
+    public const HUMIDITY_UNIT = '%';
+    public const POLLUTANT_CONCENTRATION_UNIT = 'μg/m3';
+    public const PRECIPITATION_UNIT = 'mm';
+    public const PRECIPITATION_PROBABILITY_UNIT = '%';
+    public const SPEED_UNIT = 'mph';
+    public const TEMPERATURE_UNIT = '°F';
+    public const VISIBILITY_UNIT = 'km';
+}

src/MeasurementSystem/Imperial.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace ProgrammatorDev\OpenWeatherMap\MeasurementSystem;
+
+class Imperial
+{
+    public const ATMOSPHERIC_PRESSURE_UNIT = 'hPa';
+    public const CLOUDINESS_UNIT = '%';
+    public const HUMIDITY_UNIT = '%';
+    public const POLLUTANT_CONCENTRATION_UNIT = 'μg/m3';
+    public const PRECIPITATION_UNIT = 'mm';
+    public const PRECIPITATION_PROBABILITY_UNIT = '%';
+    public const SPEED_UNIT = 'm/s';
+    public const TEMPERATURE_UNIT = '°C';
+    public const VISIBILITY_UNIT = 'km';
+}

src/MeasurementSystem/Standard.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace ProgrammatorDev\OpenWeatherMap\MeasurementSystem;
+
+class Standard
+{
+    public const ATMOSPHERIC_PRESSURE_UNIT = 'hPa';
+    public const CLOUDINESS_UNIT = '%';
+    public const HUMIDITY_UNIT = '%';
+    public const POLLUTANT_CONCENTRATION_UNIT = 'μg/m3';
+    public const PRECIPITATION_UNIT = 'mm';
+    public const PRECIPITATION_PROBABILITY_UNIT = '%';
+    public const SPEED_UNIT = 'm/s';
+    public const TEMPERATURE_UNIT = 'K';
+    public const VISIBILITY_UNIT = 'km';
+}