Add ability to switch to logarithmic scale for graphs in result tables

[nemequ]

From @nemequ on August 13, 2015 8:48

The graphs in the result table (for compression ratio, compression speed, and decompression speed) are linear, and currently can't be switched to logarithmic. It would be nice to add an interface to toggle between the two.

It would be nice if this were also consistent with the solution for #20.

Copied from original issue: quixdb/squash-benchmark#21