Adding interact.py.
Adding Interact and Lorenz examples.
Updating interact to new APIs.
Updating interact to work with latest state of widgets.
Adding .widget to function.
Get widgets from function annotations and default arguments.

Also, preserve the order of function parameters from the signature where
possible.

This uses a backport of the Python 3.3 signature machinery that @minrk
found and improved.
Renaming interact.py->interaction.py to improve imports.
Fixing interact imports.
Utter interact insanity.

This involves a bunch of really complicated logic to handle the
different ways that function parameters can be processed in Python.
Most importantly, this includes support for *args in interact.
Adding decorator forms of interact. Yeah!
Adding const pseudo-widget for fixing arguments to interact.
update interact now that SelectionWidget.values is a dict
update Interact example notebook

- use %matplotlib, not %pylab
- use non-identical graph generators in networks example
remove positional arg support from interact
move @annotate to py3compat
s/const/fixed/
ensure range widgets get value that is on a step
finish removing *args support
simplify float/int slider abbreviation logic

fixes unhanded case where only one entry is a float
fix ValueError format message