Math folder (#594)

* Move files to `Math` folder

* Allow `.DotSettings` (not `.DotSettings.user`)

* Allow the `Math` folder to ignore namespaces

.gitignore

@@ -206,4 +206,3 @@ FakesAssemblies/
 
 # Visual Studio 6 workspace options file
 *.opt
-*.DotSettings

Source/MonoGame.Extended/MonoGame.Extended.csproj.DotSettings

@@ -0,0 +1,2 @@
+<wpf:ResourceDictionary xml:space="preserve" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:s="clr-namespace:System;assembly=mscorlib" xmlns:ss="urn:shemas-jetbrains-com:settings-storage-xaml" xmlns:wpf="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
+	<s:Boolean x:Key="/Default/CodeInspection/NamespaceProvider/NamespaceFoldersToSkip/=math/@EntryIndexedValue">True</s:Boolean></wpf:ResourceDictionary>