Add support for normal diodes

[rastersoft]

This patch adds an extra parameter, --normal-diodes, that uses
normal, pass-through 1N4148 diodes instead of SMD-mounted ones.

[jeroen94704]

While I like the option for through-hole diodes, as well as your pull-request to make the switch traces optional, I think I need a better way to handle switches like these. Doing it this way quickly gets out of hand when adding more options, with the code littered with if-statements. Not sure how to approach this yet, but I'll leave both this pull-request as well as #19 open for now.