Release v0.8.0

Release v0.8.0 is ready unless we want to add anything else. Tested on OS X, Windows 8, and Ubuntu.

- Updates Node-sass, Stylus, LESS, and the LRU cache
- Adds implicit `.sass` preprocessing
- Removes Node v0.8.x as a build target for CI – Node-sass dropped it to reduce the binaries is has to ship with, and is looking towards v0.11.x instead