Improve ``single_plot()``.

Small cleanups and consistency checks.
Rewrite of plot function for multiple+stacked plots
Pass command line ``BP`` option to functions in the text module
Simpler way to format the text output template.

Also, make the template slightly shorter.
Smaller edits for consistency and readability
Add ``iplot`` function, ready for IPython Notebook.

Sucks a lot as a single-dispatch generic function though.
This is a git repo now
Update requirements for versions of Python and dependencies