kicad: convert fab.mod + add usb micro footprint
Newer versions of KiCAD treat .mod footprint libraries as "legacy" and will
refuse to edit them. This commit converts the library to the new .pretty
format.
Note that the new format is a folder with loose .kicad_mod files, so it
needs to be zipped for distribution.
Additionally, a footprint was added for the USB micro-B socket that claims to be on inventory.
