Using 'pre' command always bumps the patch version

[vortec]

It would be nice to be able to specify which part of the version should be "pre bumped". Right now, when you run 'pre' it bumps the patch version, but it's probably more realistic to pre-bump the minor or major version:

2.12.10
versionbump pre
2.12.11-dev.0

The correct behaviour is:

2.12.10
versionbump pre
2.13.0-dev.0

But there should also be explicit commands like pre-major, pre-minor and pre-patch.