ADDED a new pin electrical type "free" for internally unconnected pins.
CHANGED the "unconnected" pin electrical type is now represented by
"no_connect" in files and netlists. (The legacy syntax is also accepted
in files.)
Scope: NETLIST_ITEM, CONNECTION_TYPE, ELECTRICAL_PINTYPE,
NET_CONNECTION, NETLIST_ITEM, GRAPHIC_PINSHAPE
Note, the pin type enum had PT_ added to the front to prevent
shadowing of the INPUT symbol on msys2 (see discussion at
c17c9960d8)