Two things changed: (1) string literals can now hold backslash
escapes like "\n"; (2) MVN/MVP operands can now be prefixed with '#'.
The former was a breaking change because any string with "\" must
be changed to "\\". This is now handled by the string operand
formatter.
Also, improved test harness output. Show the assembler versions at
the end, and include assembler failure messages in the collected
output.
We have a single character-encoding test that is cloned 3x so we can
exercise the different values for the project's default character
set. It was a 65816 test because it tested 16-bit immediate char
operands, but that's a very small part of it.
The 65816-specific portion is now 20122-char-encoding. The rest is
now 201{2,3,4}0-char-encoding-X.
