Change template extension to .mako.

It doesn't look like there's anything Chameleon-specific in the
template, so should be enough for the switch to Mako.
Update template file name to .mako.
Remove config.include() of pyramid_chameleon.
Add pyramid_mako and Mako settings to pyramid.includes in ini files.
Switch dependency in setup.py from pyramid_chameleon to pyramid_mako.
Add /data directory (which will be used by Mako) to .gitignore.
Merge branch 'switch_chameleon_to_mako'

Switch from pyramid_chameleon to pyramid_mako.