Remove pkg_resources dependency

[ulif]

We use pkg_resources for retrieving package version infos. While this is not exactly bad (and even convenient from a developers point of view), it is also the only external dependency we carry with us. It would be nice, to depend on standard lib packages only, which woulg also mean less trouble for maintainers.

[htgoebel]

Beside changing the way the version is fetched, this would mean to also eliminate the entry-point mechanism used to collect the random methods. And this means, one will not be able to plug in other random sources by installing completely independent package. Is this intended?