Merge pull request #56 from spilin/master

resolve #52. Implementation of asset_path and asset_url helpers.
Update CHANGELOG.
Bump development dependencies
Update code style and expectation syntax usage.
Update GitHub pages domain.
Rework the custom Rails template hook a bit.

* Instead of checking for constants we pass flags around.
* Tilt templates live under `stylus/tilt` now.
Use a RSpec binstub to run the spec suite.
Update Hash syntax on README
Remove unused dependencies.
Wrap path with quotes in asset-url function.