Add short explanation for new tweens panel.
- Don't rely on ``pyramid.compat.json``.
Merge branch 'master' of github.com:Pylons/pyramid_debugtoolbar
add tweens panel test
add tweens png
ignore all env*
remove unused imports, change column title in tweens template
prep for 0.9.5
test performance panel with profiling on
- Address heisenbug reported where performance panel template variables cause
  unexpected results.  Can't repeat, but reporter indicates the fix works for
  him, so hail marying.
ref
belt and suspenders
rudimentary introspection ui (visit _debug_toolbar/introspection)
moar
turn introspection view into a panel
moderate
add note about introspection panel
first draft at prettifying introspection
prep for 0.9.6; add introspection png
- The performance panel of the debugtoolbar used a variable named
  ``function_calls`` which was not initialised when stats are not
  collected. This caused a ``NameError`` when mako rendered the template with
  the ``strict_undefined`` option.

Closes #48.