Add Microsemi_QFN-40-32-2EP_6x8mm_P0.5mm

I just realized that https://github.com/KiCad/Housings_DFN_QFN.pretty/pull/74 didn't get merged. See that PR for an image.

Datasheet: https://www.microsemi.com/document-portal/doc_download/131677-pd70224-data-sheet

Image: https://user-images.githubusercontent.com/1936989/32519326-3e3328c0-c3c1-11e7-999c-6e7c61c73e98.png

Notes:

• I didn't add any paste pads on the bottom layer.
• I used the pin numbering scheme @SchrodingersGat mentioned when pins are removed, and I compressed the pin numbers used to avoid any skipped pin numbers.
• Schematic symbol PR is at KiCad/kicad-library#1812.
• Footprint is used by symbol PD70224 at https://github.com/KiCad/kicad-symbols/blob/master/Power_Management.lib.

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