Comment Cleanup - Content/*.cs

Mostly just fixes for line-length and capitalization.

* There are still a number of overly long (non-comment) lines in
  ContentManager.cs and other Content 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, but now the comments are standard.