Enable git string substitution during export

Substitute dates, versions, etc when the repo is exported.
Project page URL: change from Google Code to GitHub

This project's repository is at GitHub, not at Google Code.
Change the header comments to reflect this.
Add Bokxing IT copyright string to source files touched by us
Add README.md file, adapted from original Sabre-Zarafa docs

This file shows up on the frontpage of the GitHub repo. Copy the original text
from the Sabre-Zarafa docs at Google Code, add some links, fix some typoes. Add
information about the license the code is under.