Replace gitreceive by a git plugin.

This removes the need for two distinct users.
Git pushes and dokku commands are sent using the same user.
Remove "remote:" in the git hook output
Use DOKKU_ROOT instead of HOME.

HOME is not consistent if dokku is ran e.g. as root (for setup).
The DOKKU_ROOT variable will also make it possible to have the repositories stored in an arbitrary location (works-ish right now)
Don't allow the push if building failed.
Merge pull request #270 from plietar/git-plugin

Replace gitreceive by a git plugin.
normalizing shebang and bash options. also added long-term fix for bootstrap instructions
adding a DOKKU_TRACE env var to enable "set -x"
reorganizing deploy readme
Merge pull request #275 from progrium/shebang-pipefail

normalizing shebang and bash options + long-term fix for bootstrap instructions
Remove newly introduced '0.0.0.0:' from `docker port`
Silence nginx reloading
an "installer" (really just config/setup) for prebuilt images (at least for now)
Mention issues with 13.10
merging in upstream