pip as a dependency for python modules
modular: update Readme, list dependencies and platforms
fix configure.ac bug in HAVE_PIP
fix proper AM_CONDITIONAL use in configure.ac for pip
changes to Readme based on comments to PR

thanks
Install python packages from repository cache instead of from PyPi directly.

This will make it possible to build without needing an internet connection,
speeding things up as well as maintaining better control.
Merge remote-tracking branch 'breznak/pip-install' into cached-externals
Minor spelling correction
Merge pull request #138 from oxtopus/cached-externals

Cached externals