adding set_jinja2_environment method that allow user to set Environment used in their application during configuration.
adding a set_jinaj2_environment refactoring of the build create envir…
bump up to the version.
After #84 is merged, we can think about api for setting the environment (this PR will probably need some changes).
The new pyramid_jinja2 apis use its own Environment subclass in order to define join_path. I'm not sure that an override for this is wise.