Merge pull request #2979 from davidglassborow/develop

Add link to RB Whitaker's XNA tutorials, loads of XNA / Monogame in the documentation
ImporterTypeDescription properly handles null TypeName values in Equals/GetHashCode.
Merge pull request #2987 from SickheadGames/PipelineToolNullFix

ImporterTypeDescription properly handles null TypeName values in Equals/GetHashCode.
Crash when Pipeline extensions throw InvalidContent without a ContentIdentity
Merge pull request #2989 from theZMan/develop

Crash when Pipeline extensions throw InvalidContent without a ContentIdentity