Merge pull request #11 from ryanbrainard/2xdyno

request 2x dynos for run processes
tweak docs
Add REQUEST_ID to build env and return it in Request-Id header

This is setting a REQUEST_ID env for parity with Heroku git pushes so
buildpacks can use this id as a unique value to identify builds.
Currently, it is set to the same as the slug/manifest id for
consistancy, but this could change in the future and shouldn't be
assumed to always be the same.
use quad dynos
octo dynos
read dyno size from config var
Verify cache dir exists
Merge pull request #12 from naaman/master

Verify cache dir exists