Add MFSOP-6 4 and 5 pin parts

Add MFSOP-6 4 and 5 pin parts

Using the Toshiba drawings.

Also enables definition inheritance, and corrects the README deleted_pins documentation.

Also moves Readme.md -> README.md for consistency

Relates-To: kicad-footprints#2580 because it corrects the footprint names at the same time.

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The Toshiba drawings aren't very detailed in terms of tolerances, so the pads are quite a bit thinner than the datasheet recommendation:

• https://toshiba.semicon-storage.com/eu/semiconductor/design-development/package/detail.5pin%20MFSOP6.html
• https://toshiba.semicon-storage.com/eu/semiconductor/design-development/package/detail.4pin%20MFSOP6.html

So we may want to think about that.

Existing non-generated parts on the right:

Footprint MR: kicad-footprints!3302