Making the color name to value conversion case-insensitive. Also handling the edge case of a function having the same name as a color.

Import tweaks

Fix bug in loop in Document::emit_css when size_t is unsigned.

Cleaner integration with autotools

Also allowing files to be imported without an extension. I.e., users can say "@import 'foo'" when the file is named "foo.scss".

Allowing the Document constructor to read partials (i.e., the user can say "@import 'partial.scss';" when the file is named "_partial.scss".