Add Microchip QFN entries

Footprints submitted at .https://github.com/KiCad/kicad-footprints/pull/1097.

I started a UQFN YAML file since there was already a VQFN one.

Datasheets:

• http://ww1.microchip.com/downloads/en/DeviceDoc/16L_UQFN_4x4x0_5mm_JQ_C04257A.pdf
• http://ww1.microchip.com/downloads/en/DeviceDoc/20%20Lead%20VQFN%203x3x0_9mm_1_7EP%20U2B%20C04-21496a.pdf