Feature: split mako from Pyramid

This is an experimental branch whereby the mako features are split from Pyramid, this is done in an attempt to start splitting the renderers away from Pyramid itself to make it possible to have projects that only use mako, jinja2 or chameleon and there are no extra installed packages.

This is a mostly backwards compatible change so long as the user adds `pyramid_mako`. This pull request on `pyramid_mako` https://github.com/Pylons/pyramid_mako/pull/2 would be required as well.

Documentation is still required for this change.