Add test for watching files

0.6.4 doesn't include pre-built binaries which makes it incompatible with systems
without Python installed.

Fixes #518

Install: Bind to specific binaries commit

Add ability to watch for files recursively

Add tests for indented syntax and some tweaks

Fix `--watch` option for directories

Switches out `node-watch` for `gaze` since it's used more widely

Fixes #250 and #312.

Submodules: Updated submodules (#510)

* Additions in the binding.gyp.
* Updated CLI test for line endings.
* Updated Appveyor.yml as per @FeodorFitsner's
  suggestion.

Revamp build steps

* Instead of providing the binaries with the package, it'll only download the
needed binary for the users system.
* Will only build if the tests fail.
* Move `build.js` into scripts since it's not part of the actual API.
* Move binaries to `vendor` folder to keep it separate from the rest of the code.

Fixes #504.

Run coverage programmatically

Move coverage script to Makefile

Also includes some cleanup of unnecessary files in .gitignore which should belong
in a global .gitignore.

Revert: Uses null default instead of undefined

Commit: 3b2c4954.

Minor tweaks

Rewrite lib/index.js

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