r7rs-tests: Initial commit from Chibi-scheme (tentative)
test: Add fake SRFI-64 impl on (yunisrfi s64)

We should replace this later...
Racket: Fix string buffer port impl.

Racket have native string buffer port procedures but we have to
explicitly transcode the port because racket's R6RS write/read requires
transcoded(textual) ports.

found by: Chibi-scheme test suite(R7RS)
Racket: Stub out fake SRFI-19 and replace with native

There is no clean way to import Racket's SRFI-19 into our library.
Use racket native functions instead.

(racket base) lacks monotonic times. So jiffies are not implemented.
test: (Tentative) #vu8() and Racket patched version of R7RS test