Generator cleanup

* support y.g. extend inheritance method
* use shelljs to check Slim dependencies
* use chalk for clean, better api log
* update slim generator test
* remove use of deprecated test methods

This PR also remove support for Composer and Git temporarily after
use y.g. new .extend() method. Let another generator do they job
using .composeWith() method.
Add contributor list
Merge pull request #5 from hariadi/develop

Generator cleanup