Add new visualizations and a way to pivot around the latest profile

statprof now saves all the data from the latest run to a file and allows you
to view it in different ways. Several new visualizations have been added
including a tree view with hotpath highlighting and a flamegraph view.

New usage:
    hotpath [-l --limit percent]
        Shows a graph of calls with the percent of time each takes.
        Red calls take over 10%% of the total time themselves.
    lines
        Shows the actual sampled lines.
    functions
        Shows the samples grouped by function.
    function [filename:]functionname
        Shows the callers and callees of a particular function.
    flame
        Writes out a flamegraph to ~/flamegraph.svg
        Requires that ~/flamegraph.pl exist."""