Implements Scheme Request For Implementation (SRFI) as described at http://srfi.schemers.org/
Syntax: Each <clause> should be of the form
(<feature> <expression1> …)
where <feature> is a boolean expression composed of symbols and ‘and’, ‘or’, and ‘not’ of boolean expressions. The last <clause> may be an “else clause,” which has the form
(else <expression1> <expression2> …).
The first clause whose feature expression is satisfied is expanded. If no feature expression is satisfied and there is no else clause, an error is signaled.
cond-expand is an extension of SRFI-0,
(define error slib:error)