[R6RS] syntax-case SRFI

[dyb at cs.indiana.edu]

The syntax-case SRFI is at

  http://www.cs.indiana.edu/~dyb/r6rs/syntax.html

or

  http://www.cs.indiana.edu/~dyb/r6rs/syntax.pdf

The reference implementation is missing, but I'll create one before the
SRFI is published.  It shouldn't be a big challenge to adapt the
existing portable syntax-case implementation.

Kent