Support progress-bar for learning models!

[jjfiv]

So that we have some sense it hasn't crashed without the gigantic table output...

[jjfiv]

As noted in #36, we should maybe pass Python's filehandles in. Should be easy on *nix, but I wonder about windows.

Having some sort of asynchronous learner would help with that, too, allowing python to own the print statements.

[cmacdonald]

I found https://github.com/minrk/wurlitzer:

from wurlitzer import sys_pipes
with sys_pipes():
    call_some_c_function()