POSIX leaves undefined the order of output if stderr is injected into stdout,
and in practice it differs on Windows (Linux buffers both streams separately,
Windows interleaves them as they arrive without buffering).
This should help testing on other platforms
The old error stack was fairly obtuse and hard to use for debugging.
This improves it notably by ensuring all line numbers are relative
to the file, and not, say, the macro definition.
This is a breaking change if you were parsing the old stack, but
the change should be painless, and the new stack only brings more info.
The syntax is unchanged for files, macros see their name prefixed
with the file they're defined in and a pair of colors, REPT blocks
simply append a '::REPT~n' to the context they're in, where 'n' is
the number of iterations the REPT has done.
This is especially helpful in macro-heavy code such as rgbds-structs.
c75a953 broke my (previously-working) project that defined, via
macros, 'sizeof_.player'.
A test was added to confirm that those are indeed accepted
outside of macros.
When a macro arg appears in a symbol name, the contents are appended.
However, the contents of the macro arg were not being validated.
Any character, regardless of whether it was allowed in a symbol name,
would be appended. With this change, the contents of the macro arg
are now validated character by character. The symbol name is considered
to end at the last valid character. The remainder of the macro arg is
treated as though it followed the symbol name in the asm source code.
