* benchmarks/0-reference.bm: Added as a reference benchmark to be

* benchmarks/0-reference.bm:  Added as a reference benchmark to be
used to calibrate iteration counts.

* lib.scm: Added documentation.  Added some initialization
messages.

(benchmark-time-base, benchmark-total-time, benchmark-user-time,
benchmark-system-time, benchmark-frame-time, benchmark-core-time,
benchmark-user-time\interpreter, benchmark-core-time\interpreter):
Exported.

(benchmark-time-base, time-base): Renamed time-base to
benchmark-time-base and introduced new time-base as a short-cut.

(total-time, benchmark-total-time, user-time, benchmark-user-time,
system-time, benchmark-system-time, frame-time,
benchmark-frame-time, benchmark-time, benchmark-core-time,
user-time\interpreter, benchmark-user-time\interpreter,
benchmark-time\interpreter, benchmark-core-time\interpreter,
print-result, print-user-result):  Renamed <foo>-time to
benchmark-<foo>-time.  Exceptions: benchmark-time and
benchmark-time\interpreter were renamed to benchmark-core-time and
benchmark-core-time\interpreter, respectively.