- Fix `variable_resistor` arrow such that it now has even width along the
arrow head.
- Add an "Overheight" system. Some fragments (`variable_resistor` and
`webbolt`) will now cause other fragments on the same label to preemptively
shrink down before the overheight fragment. This helps avoid
dispropotionately large text which otherwise would have to be controlled by
setting font size. This behaviour can be turned off with `--no-overheight`.