Visual Progress Bar

[saxbophone]

This would use the progress callback feature available with plot_spiral.
A simple text-based progress bar from 0-100 seems fine.
Should probably update it based on time since last update rather than whenever a new line is found.

Am tempted to have the progress bar show which exact line it is currently solving (would then go up and down as the algo goes back on itself), but this will require some changes to the library API.