Bug Fixes:
- Port various fixes from leafo/lessphp.
- Improve filter precision.
- Parsing large image data-urls does not work.
- Add == and != ops for colors.
- @if and @while directives should treat null like false.
- Add pscss as bin in composer.json (Christian Lück).
- Fix !default bug (James Shannon, Alberto Aldegheri).
- Fix mixin content includes (James Shannon, Christian Brandt).
- Fix passing of varargs to another mixin.
- Fix interpolation bug in expToString() (Matti Jarvinen).