Introduce `backup` plugin to export/import settings
Specify current backup version at the top of the script
Introduce DOKKU_ROOT and import now in git plugin
Merge pull request #265 from asm89/backup

Introduce `backup` plugin to export/import settings
Update headers
Provide more feedback for backup import
Update bootstrap.sh

A typo has been corrected.
Merge pull request #325 from ugurthemaster/patch-1

Update bootstrap.sh
Delete the /cache directory's contents from inside the container.

Fixes #322.
Buildpacks write into /cache as root, which made the delete command unable
to delete it.
Its contents are now deleted using "docker run", and thus as root.
Add support for DOKKU_TAG in bootstrap.sh

Fixes #330
Refs #329