We've been treating ASCII strings and instruction/data operands as
ambiguous, resolving low vs. high when generating output for the
display or assembler. This change splits it into two separate
formats, simplifying output generation.
The UI will continue to treat low/high ASCII as as single thing,
selecting the format appropriately based on the data. There's no
reason to have two radio buttons that are never both enabled.
The data operand string functions need some additional work, but
that overlaps substantially with the upcoming PETSCII changes, so
for now all strings set by the data operand editor are low ASCII.
The file format has changed again, but since there hasn't been a
release since the previous change, I'm leaving the file format
at v2. Code has been added to resolve the ASCII mode when loading
a v1 project file.
This removes some complexity from the assembly code generators.
