Update gulp-packages.js

I make it supports 'angular-templatecache as atc',so we can use a shorter name like pkg.atc.
Update gulp-packages.js
uninstall now works well

I rm gulp._packages to avoid conflit. 
I make packages name follow itself, and trans it to camel when we call it. it mostly like 'var name=require(pkg)' style.
now "as" works well as it.
Update README.md

enhance name rule
Merge pull request #1 from ginus/patch-1

'as' supported