Release v0.8.1 is a minor release in the v0.8 branch.

Bug fixes since v0.8.0:

fe6070c plotter: fix volcano example
a51a196 plot: fix handling of font descents

Internal and documentation fixes:

cad3ccd plotter: incorporate volcano example into package tests
de78615 plot,vg/...: make testdata regeneration easier
cf58149 cmpimg: don't report errors in helper