Extend `Thor::Group.dispatch` to always execute a single command.
Document some `Stylesheet` methods and fix the broken build.
Move most of the Stylesheet rendering helpers and logic into the Template class.

This class will act as the Public API for the custom templates to use.
Document the custom template usage on the README.
Extract the `Spriteful.options` access to a method on the Template class.
prepare for 0.3.0.beta1
Merge pull request #18 from lucasmazza/lm-custom-templates

Support custom Stylesheet templates