Add .cake extension for C#

This adds the .cake file extension to the C# language.

Here is a search in the wild: https://github.com/search?q=extension%3Acake+NOT+coffee&type=Code

Cake (C# Make) is a cross platform build automation system with a C# DSL to do things like compiling code, copy files/folders, running unit tests, compress files and build NuGet packages.

You can find out out more about cake here: http://cakebuild.net/

lib/linguist/languages.yml

@@ -392,6 +392,7 @@ C#:
   aliases:
   - csharp
   extensions:
+  - .cake
   - .cs
   - .cshtml
   - .csx

samples/C#/build.cake

@@ -0,0 +1,86 @@
+///////////////////////////////////////////////////////////////////////////////
+// ARGUMENTS
+///////////////////////////////////////////////////////////////////////////////
+
+var target = Argument<string>("target", "Default");
+var configuration = Argument<string>("configuration", "Release");
+
+///////////////////////////////////////////////////////////////////////////////
+// GLOBAL VARIABLES
+///////////////////////////////////////////////////////////////////////////////
+
+var solutions = GetFiles("./**/*.sln");
+var solutionPaths = solutions.Select(solution => solution.GetDirectory());
+
+///////////////////////////////////////////////////////////////////////////////
+// SETUP / TEARDOWN
+///////////////////////////////////////////////////////////////////////////////
+
+Setup(() =>
+{
+    // Executed BEFORE the first task.
+    Information("Running tasks...");
+});
+
+Teardown(() =>
+{
+    // Executed AFTER the last task.
+    Information("Finished running tasks.");
+});
+
+///////////////////////////////////////////////////////////////////////////////
+// TASK DEFINITIONS
+///////////////////////////////////////////////////////////////////////////////
+
+Task("Clean")
+    .Does(() =>
+{
+    // Clean solution directories.
+    foreach(var path in solutionPaths)
+    {
+        Information("Cleaning {0}", path);
+        CleanDirectories(path + "/**/bin/" + configuration);
+        CleanDirectories(path + "/**/obj/" + configuration);
+    }
+});
+
+Task("Restore")
+    .Does(() =>
+{
+    // Restore all NuGet packages.
+    foreach(var solution in solutions)
+    {
+        Information("Restoring {0}...", solution);
+        NuGetRestore(solution);
+    }
+});
+
+Task("Build")
+    .IsDependentOn("Clean")
+    .IsDependentOn("Restore")
+    .Does(() =>
+{
+    // Build all solutions.
+    foreach(var solution in solutions)
+    {
+        Information("Building {0}", solution);
+        MSBuild(solution, settings => 
+            settings.SetPlatformTarget(PlatformTarget.MSIL)
+                .WithProperty("TreatWarningsAsErrors","true")
+                .WithTarget("Build")
+                .SetConfiguration(configuration));
+    }
+});
+
+///////////////////////////////////////////////////////////////////////////////
+// TARGETS
+///////////////////////////////////////////////////////////////////////////////
+
+Task("Default")
+    .IsDependentOn("Build");
+
+///////////////////////////////////////////////////////////////////////////////
+// EXECUTION
+///////////////////////////////////////////////////////////////////////////////
+
+RunTarget(target);