Adding serialization+debug attributes to rectf
Porting my c++ interp functions to the project.

... for future UI use (since I'm on a porting binge right now). There
are currently no unit tests for anything more advanced than Lerp/Unlerp,
since they're not the simplest things to unit test and I'm not using the
functionality right now.
Finished ContentReaderX, which replaces XNA's ContentReader.

ContentReaderX is meant to be a full replacement for XNA's
ContentReader. It loads content at runtime (rather than compile time)
since I'm trying to get away from the XNA content pipeline for cross
platform reasons. ContentReaderX supports old .xnb files by passing them
to the base class for loading.