Added File > Import in which you choose a .contentproj file.
File and Build menu items now only appear as enabled when appropriate (eg, no save option if project is not dirty).
Project will now load even with broken references.
ContentItems with importers or processors which we fail to locate will now be shown as "missing".
Changing project references will now trigger content items to re-resolve their processor/importer type from the specified name.
Added documentation for classes in Microsoft.Xna.Framework.Audio
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
Comment Cleanup - Content/*.cs

* There are still a number of overly long lines in
  ContentManager.cs and other files. I'm resisting the
  urge to fix most of them, as this is a comment cleanup
  pass.

* LzxDecoder.cs: This must have been assimilated after the code
  standardization sweep.  It could use a complete run-through for
  code formatting.
Merge pull request #211 from 3vi1/monogame-sdl2

Comment Cleanup - Content/*.cs
Merge back from develop
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
Comment Cleanup - Content/ContentReaders

Most readers had no comments, and the existing ones needed few changes.
Merge pull request #212 from 3vi1/monogame-sdl2

Comment Cleanup - Content/ContentReaders
Merge pull request #2455 from Alturos/develop

Resolve PSSTexture not disposing (Issue #2122)