Merge pull request #2875 from SickheadGames/testfix

Unit Test Image Comparision Improvements
Document Point.Zero property.
Document Point.ToString() method
Document Point() constructor.
Fix typo in previous commit.
Merge pull request #2878 from dneelyep/develop

Add XML docs for a few items in MonoGame.Framework.Point.cs
Remove some #ifs
Document Rectangle's public properties and fields, and remove some whitespace for consistency.
Merge pull request #2882 from dneelyep/patch-3

Document Rectangle's public properties and fields, and remove some white...
Merge pull request #2879 from danzel/patch-1

Remove some #ifs
Some GraphicsAdapter cleanup.
Cleanup and documentation pass.
Added GraphicsAdapter.UseReferenceDevice.
Support GraphicsAdapter.UseReferenceDevice in DirectX desktop and WinStore.
Enabled GraphicsProfile.HiDef and GraphicsAdapter.UseReferenceDevice for all visual tests by default.
Merge branch 'develop' into testfix