Add support for log scale or custom scales

[thekeenant]

Currently only linear axes are supported. Perhaps some typedef which would map to a linear scale so it can be drawn like normal.

i.e. for semi-log: 10,000 -> 1.0 1,000 -> 0.75 100 -> 0.5 10 -> 0.25 0 -> 0

or for linear (the default): 10,000 -> 1.0 1,000 -> 0.1 100 -> 0.01 10 -> 0.001 0 -> 0

[thekeenant]

Added in 6fed7b1f489a7024da1145a92e217e81fcb9a6da