Ticket 330: Add R5RS compatibility library

The (scheme r5rs) library exports the standard identifiers of R5RS Scheme. By my current reckoning, those identifiers are as follows:

- * / + < <= = > >= abs acos and angle append apply asin assoc assq assv atan begin boolean? call-with-current-continuation call-with-values car case cdr ceiling char->integer char-alphabetic? char-ci<? char-ci<=? char-ci=? char-ci>? char-ci>=? char-downcase char-lower-case? char-numeric? char-ready? char-upcase char-upper-case? char-whitespace? char? char<? char<=? char=? char>? char>=? close-input-port close-output-port complex? cond cons cos current-input-port current-output-port define define-syntax delay denominator display do dynamic-wind eof-object? eq? equal? eqv? eval even? exact->inexact exact? exp expt floor for-each force gcd if imag-part inexact->exact inexact? input-port? integer->char integer? interaction-environment lambda lcm length let let-syntax let* letrec letrec-syntax list list->string list->vector list-ref list-tail list? load log magnitude make-polar make-rectangular make-string make-vector map max member memq memv min modulo negative? newline not null-environment null? number->string number? numerator odd? open-input-file open-output-file or output-port? pair? peek-char positive? procedure? quasiquote quote quotient rational? rationalize read read-char real-part real? remainder reverse round scheme-report-environment set-car! set-cdr! set! sin sqrt string string->list string->number string->symbol string-append string-ci<? string-ci<=? string-ci=? string-ci>? string-ci>=? string-copy string-fill! string-length string-ref string-set! string? string<? string<=? string=? string>? string>=? substring symbol->string symbol? tan truncate values vector vector->list vector-fill! vector-length vector-ref vector-set! vector? with-input-from-file with-output-to-file write write-char zero?

As with any library other than (scheme base), implementations SHOULD (rather than MUST) provide this.