Allow specifying a path in ++venv
Add mkvenv command, to make and activate a python venv
Add some more bits to JavaScript conceal
Various tweaks to .vimrc

* K now behaves like J, joining to the line above
* Disabled line wrapping
* Lowered scrolloff
* XML documents start not folded
`<Leader>s` adds a super() call to a python class method

It is a best-guess only. It scans upwards for a `def` statement, and
then a `class` statement, attempting to be smart about indentation. It
is not a full python parser though, and will probably fail in
interesting ways if your Python code is really dynamic and strange.