New Features: Nano, MKR WIFI, additional hole sizes and mount types

[KjellMorgenstern]

Adding support for Arduino Nano and MKR WIFI 1010. The later was tested with an FDM printer.

Please consider pull request #12, it introduces:

Variable hole sizes, since some boards have smaller mounting holes
Dual headers (HEADER_F on top, HEADER_M on the bottom) as used on the MKR WIFI 1010
Small pin (=NOTCH) that can be FDM printed, to fit the small holes from Nano and MKR boards
Spacing parameter for enclosures, so that boards that need more than 5mm can fit.

New features are added to the documentation and shown in the example.scad