[R6RS] Make -> a valid identifier

[Michael Sperber]

Many Scheme implementations allow -> as a valid identifier, usually
along with other tokens starting with -.  Since -> is such a
suggestive choice in many contexts, a lot of Scheme code out there
uses it.  I suggest we sanction this practice by doing one of two
things:

- The standard states that any token starting with - that's not a
  <number> is an <identifier>.

- We change the lexical grammar like so:

<peculiar identifier> -> + | - | ... | <dash identifier>
<dash identifier> -> - <dash subsequent> <subsequent>*
<dash subsequent> -> <initial> | <special subsequent>

I'm open to better suggestions.

Opinions ... anyone?

-- 
Cheers =8-} Mike
Friede, V?lkerverst?ndigung und ?berhaupt blabla