Add changes to support latest libsass version
Implements source map options
Exposes `sass_compile_file` function

Needed for automatic indented sass syntax recognition
Exposes `sass2scss` function
Implements precision option
Adds full sass spec test suite
Adds optional options for sass context

Source map URLs are relative to output path
Adds travis-ci configuration
Merge pull request #4 from mgreter/clean-libsass-update