Ignore deprecation warnings
Add usage string to visualizer
Use mkdtemp for workspace directory
Show rules in a table rather than a list.
Use centered boxes for the histograms.

This solves the problem of bytes read/written not showing up.
Also, bytes written/read work better with MB.
Compute optimal number of bins, fix corner cases.
Use subprocess module, allowing wait for gnuplot.
Automatic logscale/range for visualizer.

Also, cleans most tics from axis, and removes some borders.
Merge pull request #139 from btovar/visualizer-two-steps

Visualizer two steps