Migrate to gulp

To build all-in-one bundle by browserify
Update dependencies.
Build all-in-one bundle by browserify.
Use all-in-one empower and espower-source bundle for testing.
Use simple task dependencies to stop build and report on error
Stop using UMD pattern since browserify builds UMD module.
Use node.extend instead of private port of extend function.
Oh run-sequence is used by release tasks.
Farewell Gruntfile.js!
Remove unused modules
Just a semicolon
Merge pull request #11 from twada/browserify

Build all-in-one bundle by browserify