Fixes #139 - adds consistent error and warning handling for CLI and library.

* Does not throw errors anymore, instead prints them out to STDERR and exits with status 1.
* Adds two new fields to CleanCSS objects - warnings and errors.
* Updates imports/inliner.js to not act as a singleton.
* Adds 'both root and output file given' warning to inliner.
Rearranges History.md a bit.
Add bin/cleancss to the JSHint command and fix the warnings.
Update JSHint's options.

Enable indent option and move multistr option where is needed only.
Enable JSHint's `eqeq` rule.

http://www.jshint.com/docs/options/#eqeqeq

This way we are consistent.