Remove contrib/ssh-agent as it has been documented
docs: Minor tweak
docs: Update getting started to use the official pg image
buildpacks/all: Use a specific cache dir for each platform
buildpacks/ruby: Looks like the heroku buildpack installs bundler for us
buildpacks/ruby: Configure bundler globally in order to fix GH-64
buildpacks/ruby: Rollback to the rvm implementation [GH-58]

The custom buildpack got out of control, there's way to many hacks
around, I've had issues like GH-64 and the rvm version is a lot simpler.
We can always revisit this in the future though.

Oh, and BTW, this fixes GH-64
buildpacks/ruby: Theres no need to install nodejs, the base image already have it around