* Introduce explicit serpentine: bool argument instead of using negative
numbers (thanks, ghost of @tannewt sitting on one shoulder)
* Fix several calculations of height
Testing performed (matrixportal):
* set up a serpentine 64x64 virtual display with 2 64x32 tiles
* tried all 4 rotations
* looked at output of REPL
This gets all the purely internal references. Some uses of
protomatter/Protomatter/PROTOMATTER remain, as they are references
to symbols in the Protomatter C library itself.