Generate prerelease compatible RPM version numbers and release numbers - 662

I think this should produce numbers that follow the guidlines here:
 * http://fedoraproject.org/wiki/Packaging:NamingGuidelines#Pre-Release_packages

There seem to be one or two warning when I build this locally with mock and test with rpmlint so it'll be interesting to see what buildbot says.

```
[~/.../HybridLogic/flocker-0.1.3pre1]$ rpmlint /var/lib/mock/fedora-20-x86_64/result/python-flocker-0.3.0-0.1.dev.fc20.src.rpm 
python-flocker.src: W: spelling-error %description -l en_US multi -> mulch, mufti
python-flocker.src: W: spelling-error %description -l en_US frontend -> fronted, front end, front-end
python-flocker.src:121: W: macro-in-%changelog %{version}
python-flocker.src:121: W: macro-in-%changelog %{release}
python-flocker.src: W: invalid-url Source0: Flocker-0.3.0dev1.tar.gz
1 packages and 0 specfiles checked; 0 errors, 5 warnings.
```

I tested this by adding various local tags to a local git clone of a clone to avoid any chance of pushing testing tags to GitHub.

Fixes #662 
I think it probably isn't worthwhile to update this changelog. Every commit to the repository creates a new version, and we aren't going to put all those version here.

If we were going to update this changelog, we should keep the automatically generated entry be "Development version", and put the changes after that. But I don't think it is worth it. If people want the history, they can just look at the git log.