Build: Add v8 specific platform builds

Idea courtesy of node-fibers.
When installing, check to see if there is a compatible binary version
for the current version of v8. v8 3.6 = Node 0.6, 3.11 = Node 0.8, 3.14
= Node 0.10. The test suite is run as well, so that any underlying
libsass breaks will be rebuilt.

Closes gh-146