Weave-minimal

Another maintenance release which features:
- replace `optparse` with `argparse` for nice `--help` generation
- better CLI documentation
- remove deprecated `--prefix` option, use `--base-url` instead
- support _real_ concurrency via [gevent](http://gevent.org/)
- support for uWSGI and Gunicorn (only one process though, see [Deployment](https://github.com/posativ/weave-minimaldeployment))
- ship _scratch.png_ with weave-minimal to avoid plain-text connections to http://posativ.org/scratch.png (suggested via mail)

Almost a year after the initially working code, I'm quite proud to release a stable version. The lightweight sync server is compliant to Mozilla's Storage API 1.1 and User API 1.0. Both APIs remain used for another 6 months at least.

New features
- stable API implementation
- support for Python 3.3+
- multi-threaded internal WSGI server
- limit request size to 512k (both APIs only use 256k + a few bytes overhead)