Added XC6SLX16 PiSwords dev board#191

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DaveBerkeley wants to merge 5 commits intoamaranth-lang:mainfrom

DaveBerkeley:main

Commits on Jan 17, 2022

Added XC6SLX16 PiSwords dev board
DaveBerkeley
committed

Commits on Jan 20, 2022

fixed error in connector strings for pislx16.py
DaveBerkeley
committed

Commits on Feb 5, 2022

Added sdcard io to pislx16.py
DaveBerkeley
committed

Commits on Feb 22, 2022