Update pyenv and add new versions

Thanks for this module - I have a pull-request you might like to incorporate.

- bumped the pyenv version to a more recent version. I haven't chosen latest as I've got anecdotal evidence that it will cause the 3.3.3 build to fail on OSX.
- updated in-module pyenv-install script to the version in that updated version of pyenv.
- added definitions for 2.6.9, 2.7.6, 3.1.5, 3.2.5, 3.3.3
- updated `python::2_6`, `python::2_7`, `python::3_3` to the latest versions in their series