baseimage: apt-get clean after install
baseimage: Install ruby (and possible other programming language envs) dev dependencies
buildpacks/ruby: No need to specify HOME anymore
buildpacks/ruby: Configure ~/.gemrc to disable ri / rdocs installation

Closes GH-5
buildpacks/ruby: Uninstall bundler 1.5.0 before installing 1.5.2
buildpacks/ruby: Redirect bundler upgrade output to /tmp/build.log
stack: Move builder script around
stack: Rename load env script to match whats in use by the image
baseimage: Better structure for stack and Dockerfile
buildpacks/golang: Improved output
stack/build-project: Clean up $cache_root if configured
buildpacks/inline: No longer needs a bin/detect script on project dir to work

Closes GH-10
buildpacks/ruby: Fix GH-8 (properly check whether ruby is already installed or not)
buildpacks/ruby: Show trailing /tmp/build.log lines in case of error

Fixes GH-6
builder: Accept list of buildpacks to compile as the -b parameter

Closes GH-15
stack/my-init: Disable envvars import / export for now
cli: Give users a chance to commit a bootstraped container that has exit code != 0

Closes GH-16
buildpacks/php: Install dev dependencies with composer
buildpacks/php: Do not require composer.lock to be present
buildpacks/php: Cache composer packages on CACHE_DIR/composer