Version numbers in 3 places

[paul-krohn]

There are version numbers in 3 places, I intend to fix this by refactoring into a module structure, and just want to be sure @crccheck and @tmclaugh are aware.

[crccheck]

There's a make version to facilitate maintaining version number. It's an unusual pattern, but I found I like it because:

• I really hate it when I open setup.py and I can't see a version number
• I also really hate import magic to get the version from somewhere else into setup.py
• all the other python ways I've seen of maintaining versions are more verbose ways of doing sed. Just because it's a Python project doesn't mean it has to be 100% Python.

Some things I would change if I had to do it over again:

• have a VERSION file. This makes it easy for external tools to just cat VERSION to get the version
• import version from leadbutt into plumbum. Because those two versions are linked, it's more explicit to see that import statement to mean: match versions
• add an os check to use gsed instead of sed on OSX because BSD sed is different.