WIP fixes to FontDescriptionProcessor.
Merge branch 'FontProcessor' of https://github.com/SickheadGames/MonoGame into FontProcessor
Merge branch 'develop3d' into FontProcessor

Conflicts:
	MonoGame.Framework.Content.Pipeline/MonoGame.Framework.Content.Pipeline.Windows.csproj
Merge branch 'develop3d' into FontProcessor
Merge branch 'FontProcessor' of https://github.com/SickheadGames/MonoGame into FontProcessor
Prevent the importer from adding duplicate characters.
Removed outdated comments
Workaround that allows generic readers to be looked up.
First functional SpriteFontDescription .xnb written.
Merge branch 'FontProcessor' of https://github.com/SickheadGames/MonoGame into FontProcessor
Merge branch 'develop3d' into FontProcessor
Removed unnecessary #usings.
Miscommit. Removed unused helper class.
Removed unnecessary comment for testing.
Merge branch 'develop3d' into FontProcessor
Removing workarounds.
Merge branch 'develop' into FontProcessor
SpriteFontContent no longer derives from ContentItem.
Moving SpriteFontContent back to the Processors folder.
Merge pull request #1383 from SickheadGames/FontProcessor

First working SpriteFontDescription .xnb written