Move version parsing into semantic_version or semver

[jayvdb]

I guess you ran into a few of the bugs in semantic_version wrt npm ranges, and had to create your own parser.
e.g. rbarrois/python-semanticversion#62

It does intend to support npm's advanced range syntax, but the project appears moribund atm.

There is also willingness to support the advanced range syntax at python-semver/python-semver#25 , but reasonably the maintainer wanted it to be separate from the simple syntax.