raw string literal reader extension

[Daniel Llorens]

Hi, 

https://github.com/lloda/guile-raw-strings

is a reader extension to be able to write string literals verbatim, without 
escapes. E.g. you can write

#R-(quotes " and escapes \ and newlines
           can " freely be used " here)-

where you'd normally need escapes:

"quotes \" and escapes \\ and newlines\n           can \" freely be used \" 
here"

This comes in handy for docstrings, regexps, etc.

The delimiters are arbitrary strings (so - above). I took this from one of the 
varieties of C++ raw string literals [variant (6) in 
http://en.cppreference.com/w/cpp/language/string_literal] as it seems to be the 
most flexible take. In other variants the delimiters are fixed, so one would 
still need to escape certain characters.

On the Scheme/Lisp side I'm not aware of anything standard, but a quick search 
shows stuff like 
http://mihai.bazon.net/blog/hashes-and-raw-strings-in-common-lisp or 
https://github.com/cmpitg/racket-raw-string, where the delimiters are either 
single characters or certain delimiter pairs. It's trivial to modify the 
present extension to work in that way.

Anyway, I hope some of you can find this useful.

Regards

        Daniel