ronn --version probs: no ".pre" part, bogus GitHub URL for untagged releases, doesn't reflect add'l commits/changes

[apjanke]

Here's what ronn --version does when you've bumped the version string in the source code.

$ ./bin/ronn --version
Ronn-NG v0.10.1
http://github.com/apjanke/ronn-ng/tree/0.10.1.pre4

If you haven't yet created that tag or release in GitHub yet, you get a 404 page for it.

Maybe we want to change the output for in-progress releases here. And maybe add an indicator for when it's running from a git commit that's not tagged as a version, including both additional commits and local changes.

Also, the version string in ronn --version doesn't include the ".preN" suffix for prereleases. Should probably add that; I like the version string to exactly reflect what you're running.