addons/docker: Some minor tweaks

* Do not symlink subsystem if already symlinked
* Skip `chown` on docker root dir to prevent issues related to using sudo within nested containers
cli: Remove bash version in favor of using the new Golang CLI

Closes GH-70, GH-27, GH-54
baseimage: Switch to progrium/cedarish:cedar14
buildpacks/golang: Update default version to 1.3.1

Closes GH-72
baseimage: Shorten PS1

Closes GH-71
Base auto-build image from v0.2.0
baseimage: Shrink image size a bit more
baseimage: Install nodejs, mercurial and bazaar so that we dont have to deal with that on Rails / Golang projects

On a future release we'll install them on demand but this will do the
trick for now
Update CHANGELOG
contrib/squid3-ssl: Update to new plugin format
Dogfooding
properly inject custom POSTGRESQL_DATA into POSTGRESQL_CONFIG_FILE
actually sed injection of POSTGRESQL_DATA needs to be done as root
Merge branch 'rvalyi-master' into next
addons/postgresql: Tweak POSTGRESQL_CONFIG file only if the POSTGRESQL_DATA is different from the default [GH-79]
addons/postgresql: Fix for GH-78
buildpacks/ruby: Make use of Heroku rubies instead of using RVM

Closes GH-69
buildpacks/ruby: Add support for Heroku cedar rubies [GH-69]
buildpacks/ruby: Support parsing ruby version from `.ruby-version`

Closes GH-41
buildpacks/ruby: Bump default installed version to 2.1.3