Feature/sourcemaps and tests

Added the ability for node-stylus-renderer to write sourcemaps (added in Stylus 0.48.0)

@bengourley The code you already reviewed remains unchanged, but I had to overhaul the tests (with some help) to allow for multiple generated files for some tests (css + css.map). Thought I'd let you see this before publishing – happy to make further changes if needed.

Bonus: 
Added .jcsrc and .jshintrc to tidy up a bit.
Test for passing through an array of stylus files.