Rewrite lib/index.js

Move source files to src/ and sass-spec to test/fixtures/spec

Cleanup build.js and move it to lib

Cleanup CLI

Build: Verbose stats

Build: Uses different strategy to test bins status

Cleanup tests

Only 90% of the test should pass.

Don't rely on isTTY for stdin/stdout

Misc. Fixes

Also updated sass-specs.

Actually isTTY is only relevant if we want to see whether we really have to read from stdin.

If isTTY is falsey (i.e. empty), the cli will attempt to read from stdin even if it is passed an input filename.

As assert aborts the code execution if the file exists, this test will result in the file not being deleted if it exists. This change makes sure the file is cleaned up if it exists, before the assert has a chance to abort.