Without pygments doc8 will throw "errors" since it cannot check code
blocks. Pygments has since been added to the dependencies upstream [1],
though that hasn't made it into a release yet. I think we should already
adopt this now.
[1] b693181658
The `buildPython*` function computes name from `pname` and `version`.
This change removes `name` attribute from all expressions in
`pkgs/development/python-modules`.
While at it, some other minor changes were made as well, such as
replacing `fetchurl` calls with `fetchPypi`.
