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