Ignore vim swap files
Initial python virtualenv wrapping functionality

slingpie executable: given the path to a virtualenv as sole input,
creates a temporary directory and makes a munged, easily relocatable
version of that virtualenv within the temporary directory.
  TODO: add streaming support for output as a zipped tarball.

venv package: basic structures/interface for wrapping the virtualenv.

util package: for now, filesystem helpers, like recursive copies.

exec package: functions and template for assembling the executable
entry point that all the venv's bin/* members will refer to.

A total absence of unit tests leaves me sad, but hey, I'm just
learning go.  Baby steps.