Overhauled `module/xplm': pyenv, rbenv, plenv

The Python, Ruby, and Perl module managers are complete

This means that `rbenv', or `python-virtualenv' are no longer
os-level package dependencies; instead the `xplm' module takes
responsibility of installing anything to do with Ruby, Perl, or
Python via their respective `*env' virtual environment utilities,
including the installation of those utilities themselves.