Mark "syntax outline" code listings as Swift (#44)

Without any language in the markdown, they don't get syntax highlighting.

Author: amartini51

.gitignore

@@ -2,3 +2,4 @@
 .swiftpm
 /.build
 /Package.resolved
+.docc-build

Sources/TSPL/TSPL.docc/LanguageGuide/Closures.md

@@ -134,7 +134,7 @@ using closure expression syntax.
 
 Closure expression syntax has the following general form:
 
-```
+```swift
 { (<#parameters#>) -> <#return type#> in
    <#statements#>
 }

Sources/TSPL/TSPL.docc/LanguageGuide/CollectionTypes.md

@@ -192,7 +192,7 @@ which is a shorthand way to write one or more values as an array collection.
 An array literal is written as a list of values, separated by commas,
 surrounded by a pair of square brackets:
 
-```
+```swift
 [<#value 1#>, <#value 2#>, <#value 3#>]
 ```
 
@@ -1142,7 +1142,7 @@ the key and value in each key-value pair are separated by a colon.
 The key-value pairs are written as a list, separated by commas,
 surrounded by a pair of square brackets:
 
-```
+```swift
 [<#key 1#>: <#value 1#>, <#key 2#>: <#value 2#>, <#key 3#>: <#value 3#>]
 ```
 

Sources/TSPL/TSPL.docc/LanguageGuide/ControlFlow.md

@@ -306,7 +306,7 @@ a set of statements is repeated until the condition becomes `false`.
 
 Here's the general form of a `while` loop:
 
-```
+```swift
 while <#condition#> {
    <#statements#>
 }
@@ -508,7 +508,7 @@ It then continues to repeat the loop until the condition is `false`.
 
 Here's the general form of a `repeat`-`while` loop:
 
-```
+```swift
 repeat {
    <#statements#>
 } while <#condition#>
@@ -794,7 +794,7 @@ for responding to multiple potential states.
 In its simplest form, a `switch` statement compares a value against
 one or more values of the same type.
 
-```
+```swift
 switch <#some value to consider#> {
    case <#value 1#>:
       <#respond to value 1#>
@@ -1602,7 +1602,7 @@ a label on the same line as the statement's introducer keyword, followed by a co
 Here's an example of this syntax for a `while` loop,
 although the principle is the same for all loops and `switch` statements:
 
-```
+```swift
 <#label name#>: while <#condition#> {
    <#statements#>
 }
@@ -1922,7 +1922,7 @@ for the full list, see <doc:Attributes#Declaration-Attributes>.
 In addition to specifying major version numbers like iOS 8 or macOS 10.10,
 you can specify minor versions numbers like iOS 11.2.6 and macOS 10.13.3.
 
-```
+```swift
 if #available(<#platform name#> <#version#>, <#...#>, *) {
     <#statements to execute if the APIs are available#>
 } else {

Sources/TSPL/TSPL.docc/LanguageGuide/ErrorHandling.md

@@ -395,7 +395,7 @@ to determine which one of them can handle the error.
 
 Here is the general form of a `do`-`catch` statement:
 
-```
+```swift
 do {
     try <#expression#>
     <#statements#>

Sources/TSPL/TSPL.docc/LanguageGuide/Initialization.md

@@ -922,7 +922,7 @@ will save time or make initialization of the class clearer in intent.
 Designated initializers for classes are written in the same way as
 simple initializers for value types:
 
-```
+```swift
 init(<#parameters#>) {
    <#statements#>
 }
@@ -933,7 +933,7 @@ Convenience initializers are written in the same style,
 but with the `convenience` modifier placed before the `init` keyword,
 separated by a space:
 
-```
+```swift
 convenience init(<#parameters#>) {
    <#statements#>
 }

Sources/TSPL/TSPL.docc/LanguageGuide/TheBasics.md

@@ -1411,7 +1411,7 @@ as part of a single action.
 
 Write an optional binding for an `if` statement as follows:
 
-```
+```swift
 if let <#constantName#> = <#someOptional#> {
    <#statements#>
 }

Sources/TSPL/TSPL.docc/ReferenceManual/Attributes.md

@@ -13,7 +13,7 @@ the compiler shouldn't generate a warning if the return value is unused.
 You specify an attribute by writing the `@` symbol followed by the attribute's name
 and any arguments that the attribute accepts:
 
-```
+```swift
 @<#attribute name#>
 @<#attribute name#>(<#attribute arguments#>)
 ```
@@ -77,7 +77,7 @@ including important milestones.
   of the specified platform or language in which the declaration was introduced.
   It has the following form:
 
-  ```
+  ```swift
   introduced: <#version number#>
   ```
   The *version number* consists of one to three positive integers,
@@ -86,7 +86,7 @@ including important milestones.
   of the specified platform or language in which the declaration was deprecated.
   It has the following form:
 
-  ```
+  ```swift
   deprecated: <#version number#>
   ```
   The optional *version number* consists of one to three positive integers,
@@ -100,15 +100,15 @@ including important milestones.
   it's removed from the specified platform or language and can no longer be used.
   It has the following form:
 
-  ```
+  ```swift
   obsoleted: <#version number#>
   ```
   The *version number* consists of one to three positive integers, separated by periods.
 - The `message` argument provides a textual message that the compiler displays
   when emitting a warning or error about the use of a deprecated or obsoleted declaration.
   It has the following form:
 
-  ```
+  ```swift
   message: <#message#>
   ```
   The *message* consists of a string literal.
@@ -118,7 +118,7 @@ including important milestones.
   when emitting an error about the use of a renamed declaration.
   It has the following form:
 
-  ```
+  ```swift
   renamed: <#new name#>
   ```
   The *new name* consists of a string literal.You can apply the `available` attribute
@@ -198,7 +198,7 @@ If an `available` attribute only specifies an `introduced` argument
 in addition to a platform or language name argument,
 you can use the following shorthand syntax instead:
 
-```
+```swift
 @available(<#platform name#> <#version number#>, *)
 @available(swift <#version number#>)
 ```