Scripted alternative to #489 (QFN-24-1EP_4x4mm_EP2.7x2.7)

This is the scripted replacement to #489

Commit introducing this part to the script: https://github.com/pointhi/kicad-footprint-generator/pull/125/commits/86e41b9132bb0f6318095f846296aa4f61e06188

Used for symbols in PR: https://github.com/KiCad/kicad-symbols/pull/426 Datasheet used (The other two do not show tolerances): http://www.alfarzpp.lv/eng/sc/AS3330.pdf

Dimensioned drawing (Of the version without rounded rectangle as stepup does not support rounded rectangle pads)

I also added a thermal via version. (As these seem to be used for voltage regulators i assume heat transfer would be quite important.) I chose quite a lot vias (3x3) which means avoiding vias with paste is not really possible. So i increased the paste coverage to ~75% to compensate for paste wicking.