Fix warnings

Fixes the warnings thrown by the compiler by our library. Changes include:
* Getting rid of a ton of unused imports and variables
* Refactoring the ParseFlags struct in parse.rs to have the u attribute be lowercase
* Un-publishing the parse module (I am not sure why it was ever public in the first place?) in libr.rs
* Publishing some imports of private types that were being used in public methods and constructors (specifically, Ranges, ParseCodes, and ParseFlags)