Added gyp submodule.
Allow compilation directly from git.

Fixes #89. Make sure to add submodules: true to your Gemfile.
Separated code checkout to a module.

This will make sure the right version of the code will be shipped in the gem
and the right version will be used when compiling directly from git.
Add version require to checkout module.
Make sure .applied_patches is removed when recompiling v8.
Fix location_spec failure with rspec 2.14
Add instructions for using the git repo as a gem source