Trim whitespace
Fix incorrect link to github repo
Add deprecation note in commentary
Add deprecation warning to virtualenv-workon

Include links for alternate packages:

    pyvenv:             https://github.com/jorgenschaefer/pyvenv
    virtualenvwrapper:  https://github.com/porterjamesj/virtualenvwrapper.el
    python-environment: https://github.com/tkf/emacs-python-environment
Bump version number and date