Added documentation for classes in Microsoft.Xna.Framework.Audio
Doc updates for Microsoft.Xna.Framework.Audio.
Update AudioCategory.cs
Update InstancePlayLimitException.cs
Update NoAudioHardwareException.cs
Handle texture filter type "None" to force no mipmaps.
Update SoundEffect.cs
Update SoundEffectInstance.cs
Merge pull request #2458 from SickheadGames/PipelineTool

PipelineTool, Import XNA project
-16 is a more reasonable default.
Merge pull request #2459 from SickheadGames/nomip

Support Texture Filter None
Update NoAudioHardwareException.cs
Merge pull request #2457 from SickheadGames/Documentation

Audio Docs
Fixed a bunch of cases of internals being public.
Fixed incorrect DLL for Win8 docs.
Fixed incorrect parameter name in docs.
Fixed incorrect parameters in GetVariable().
Trying to fix Mac build which seems to not like an internal extension class.
Converted VertexElementFormat and SurfaceFormat size extension methods to plain static methods to please the MacOS build which seems to not line internal extension classes.
MGCB will not try to make output/intermediate directories relative to the project if they are already rooted.