* Add documentation to overview.
* Clean up asterisk placements in variable declarations.
* Add appledoc section headers.
* Reorganize methods and properties for documentation clarity.
* Fill in missing documentation, parameter definitions, and return values.
* Clean up whitespace inconsistencies.
* Builds on work started by @OpenFibers.
* Should eliminate all cache warnings.
* Added FileMD5Hash library for efficiently computing MD5 for files
* Extended RKParams to return composite MD5 for all attachments
* Implemented MD5 method on each RKParamsAttachment instance
* Updated RKRequest to utilize new MD5 sums and enabled cache keys for RKParams
