[R6RS] Unicode scalar value escape sequences

[William D Clinger]

Mike Sperber wrote:
> If it's all about reading, I propose requiring 2, 4, and 6 digits,
> respectively, at least in strings, and adding the #\x syntax.

I'd also suggest that the proposal address how Scheme's standard
DISPLAY and WRITE procedures should print strings.  The point
here is that semi-obsolete escape sequences can be supported
for reading but not directly supported for writing.

Will