Presentation Console: prescons.py

This is a "pseudo-interactive" python console for giving presentations that
involve some live coding.  It reads code from an input file and runs it line by
line.  You can move through the code by hitting the space bar.

You can also switch to (and from) a normal interactive console by pressing
Ctrl-C.  This allows you to inspect, and even make changes to, the console's
environment in the middle of a presentation.

There is a video of it in action, for my Europython talk on the descriptor
protocol, at youtube.com/watch?v=D3-NZXHO5QI.  The input file can be found at
github.com/inglesp/Discovering-Descriptors/blob/master/descriptors.py.

Suggestions, bug reports, patches welcome at github.com/inglesp/prescons.

Usage:

 $ python prescons.py <filename>

Alternatively, install the library from PyPI (eg with $ pip install prescons)
and then run:

 $ python -m prescons <filename>

Tested on Posix and Windows, and with pythons 2.7 and 3.2+

Thanks to Asim Ihsan (github.com/asimihsan) and Tom Close (github.com/TomClose)
for testing and ideas.
