Watch files and recompile on changes 

Resolve #15.

Example:

    ember-precompile *.handlebars -f templates.js -w
    
When watching, `ember-precompile` will now automatically watch any referenced files for changes and recompile the output upon any changes to reference files.

Pull request includes the following changes:
- Passing argument `-w` indicates to watch specified files for changes and re-compiles them.
- Added new node module dependency, colors, for better logging. 
- Included details in README.
- Bumped version number. 
- Added self as contributor.