This touches up a handful of places in the python documentation to try to make
the current best-practices more obvious. In particular, I often find the
function signatures (what to pass, what not to pass) confusing and have added
them to the docs.
Also updated the metas to be more consistent with the most frequently used
modern style.
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`.
