Reference implementation for a git-aware deployment process.

This script will:

• clone the repository on the local machine or fetch if it already exists
• reset hard to the specified revision
• carefully update the submodules
• rsync the checkout (minus .git/) to the deployment directory
• update the symlink
• restart the webserver

Note that this is a reference implementation -- it's to help you build this logic into your own deployment process, not to be a standalone deployment script.