March 9, 2022:  First draft of the open_pdks installer for the Global Foundries
gf180mcu (180nm) open PDK.

July 27, 2022:  Open source repositories now available on github, so integrating
directly into open_pdks.

February 14, 2023:  Added PDK variant gf180mcuD, which is like gf180mcuC except
has a top metal thickness of 1.1um instead of 0.9um.  According to GF, this is
preferred for better wire bonding yield on the pads.  The first open MPW was
done with gf180mcuC, but all subsequent open MPWs will be done with gf180mcuD.