Create additional frameworks

I wanted to be able to leverage the power of IB_DESIGNABLE/IBInspectable.  This commit allows you to pass over custom frameworks during project generation, which is incredibly handy.

Example in your project Rakefile:
`app.vendor_project('frameworks/DesignableKit', :static, { ib: true })`

passing `ib: true` in the opts for vendor_project will create a custom framework for you.

Try this simple gist, and put the files in `frameworks/DesignableKit`
https://gist.github.com/malkomalko/09688f2880bd7a879a17

Rejoice! http://quick.as/rm6kixgg
Wow, that friggin' simple!?  Again, nice work!

(also: I like the 'single line `extra_frameworks`' method :smiley:)