Use aslist instead of custom filter
Add future_imports as a configurable

This allows a user to set future_imports in their configuration file,
and have those automatically passed on to Mako.

Closes #22
Add tests for future_imports
Add extra tests for aslist change
Add extra intersphinx entries
Add documentation about future_imports
Update CHANGES.txt
Merge branch 'feature.future_imports'

This adds in the ability to specify future imports that are
automatically added to all new mako templates.

Closes #22
Update CHANGES.txt for 1.0
Prep for 1.0