Merge pull request #2377 from thefiddler/angle

RFC: Add support for ANGLE platform (take 2)
Modification for MacOSX mouse wheel support.  This fixes Open Issue https://github.com/mono/MonoGame/issues/2276.
Merge pull request #2452 from mono/xamarin

Modification for MacOSX mouse wheel support.  This fixes Open Issue http...
Remove VertexElementDeclaration fixes #2304
Fix a few more minor warnings. (Shader change from @flibitijibibo)
Merge pull request #2453 from danzel/fix-2304

Remove VertexElementDeclaration
Merge pull request #2454 from danzel/more-warnings

Fix a few more minor warnings
Resolve PSSTexture not disposing (Issue #2122)

Properly dispose of PSM's _textrue2D Fixes #2122
Correct issue where PSM SpriteEffect.cgx was named incorrectly
Create README.md

First pass at a documentation writing guide.
Update README.md

Spelling fixes.
Update README.md

Some formatting cleanup.
Update README.md

Small formatting changes.
Update README.md
Merge pull request #2455 from Alturos/develop

Resolve PSSTexture not disposing (Issue #2122)
Merge branch 'develop' into PipelineTool
Merge branch 'develop' into PipelineTool
Working on making PipelineProject.References editable.
Doc updates for Microsoft.Xna.Framework.Audio.
PipelineProject.References now editable in a separate dialog (rich text box). Properly notifies the controller when it is modified.
Added automatic remapping from old "MG.." style processor names to new names.
Importing of XNA projects should now be fully functional.
Update AudioCategory.cs