R6RS Strings

[Mike Gran]

Hi-

I've been playing a bit with the R6RS concept of character and string escapes.
I think there are a couple of fairly easy things we could do to help
support them.

First off, there are a couple of missing escapes: the named characters
#\alarm, #\linefeed, #\vtab, and #\delete, and the string escape "\b"
for backspace.

Second, what do you think about making a reader option to change the
input and output format of string and character escapes to the R6RS escapes?

Characters would be #\xNNN, where NNN is a hexidecimal number of one
to 9 (!) digits, even though 6 digits is always sufficient.

String escapes would become "\xNNN;" where, again, NNN is a hex number of
variable length, and where there is a terminal semicolon ';'.

(For those that don't recall the discussion, the character and string
escapes in Guile 1.9 were designed not to break code written for 1.8.x,
which is why they don't follow R6RS.  They also leverage some of the
libunistring behaviors.)

Lastly, there is also a rather bizarre 
\<intraline whitespace><line ending><intraline whitespace>
escape sequence in R6RS, which could be incorported, I guess.

-Mike Gran