Clean up documentation and formatting in RKURL header and implementation.

* Add documentation and example to overview.
* Add appledoc section headers.
* Fill in missing documentation, parameter definitions, and return values.
* Clean up whitespace inconsistencies.
* Remove appledoc significant asterisk in non-documenting comment.

Code/Network/RKURL.m

@@ -131,7 +131,7 @@
 
 #pragma mark - NSURL Overloads
 
-/**
+/*
  Overload implementations from NSURL. We consider a naked string to be initialized
  with a baseURL == self. Otherwise appending/replacing resourcePath will not work.
  */