Put Apache-2.0 license at LICENSE
Add Apache license header to lots of files

- I added it to no documentation files [this appears to be what OpenStack
  does.]

- I did not add it to haas/__init__.py, but did add it to
  haas/drivers/__init__.py .  This is because the former is empty.  (This is
  what OpenStack appears to do.)

- For more information, see the following:

    https://www.apache.org/licenses/LICENSE-2.0.html#apply
    https://www.apache.org/dev/apply-license.html#new
Update AUTHORS file

I did this by running: 'git log --format="%aN <%aE>" | sort | uniq', manually
removing non-people, and manually deduplicating people who have committed with
more than one email, such as Zhaoliang.
Merge pull request #183 from gsilvis/license

Update licensing