[Feature request] numeric escape sequences in strings

[JL2210]

Numeric escape sequences in strings such as e.g. \000 \xff (in particular, the former) might be useful for automatic code generators so that they don't have to output an additional zero outside of the string.

Example:

  db "Hello, World!\x00"

[Rangi42]

You can do charmap "$x00", 0 and then db "Hello, World!$x00". This avoids storing arbitrary bytes in strings during rgbasm processing (so they stay as valid UTF-8 encoding), and only does the charmap-to-byte conversion when inserting bytes into the ROM.

Actually storing arbitrary bytes in strings is a matter for #938.

[aaaaaa123456789]

Octal strings are impossible to add: \1, \2, and so on are macro expansions.

That being said, there's a bigger underlying problem here: the source character set doesn't match the output character set. The existence of charmap means that you cannot be sure that db "abc" will be equivalent to db $61, $62, $63 unless you control the full source of the translation unit. Automatic code generators often cannot make that assumption in the first place.

And if you control the full source of the translation unit, you can define your own escape sequences (perhaps in an included file) and just use them anywhere. Backslashes aren't available, but you can use literally any other character:

  charmap "``", $60 ; first of all, have the backtick escape itself
  charmap "`n", $0a
  charmap "`t", $09
  charmap "`x00", $00
  charmap "`x01", $01
  ; ...and so on

[Rangi42]

That can even be automated:

	charmap "``", $60
	for n, 256
		charmap "`x{02x:n}", n
	endr

[ISSOtm]

Should this be closed, then?