Added built-in System and Math content type writers.
Reader type is now correctly derived from writer type.
Merge branch 'develop3d' of https://github.com/mono/MonoGame into pipeline
Merge branch 'develop3d' of https://github.com/mono/MonoGame into pipeline
Merge pull request #1276 from slygamer/pipeline

Add built-in System and Math content type writers
Merge pull request #1277 from Shqrdx/develop3d

Test commit for MonoGameTeam. Added comments to MathHelper.
Added some tests to check for SDK's before building
Fixed issue with build script
removed call to installer as that will be a seperate task
Added missing content type writer source files.
Merge branch 'develop3d' of https://github.com/mono/MonoGame into pipeline
Merge pull request #1279 from slygamer/pipeline

Added missing content type writer source files.
Fix incorrect use of Dispose in ShaderProgramCache
The finalizer was telling Dispose(bool) to dispose of managed objects, which is incorrect.  This was causing a crash on exit.
Merge pull request #1281 from slygamer/shaderprogramcache-dispose

Fix incorrect use of Dispose in ShaderProgramCache