Beware of bad documentation.  operator--(int) does not return what
the header claimed it did.

Generally, opaque data operations are expected to be over 'void *' and have
now converted interfaces to do that.  Update() method honors millisecond limit to dwell
time.  Might want to homologate the millis/uSecs mix later....

chunking data.  Remove the stateful use of a seek pointer so
that shared read is possible (though maybe not interesting).

The unit/integration tests don't work yet as I'm still battling cmake/autobuild
as usual but first milestone passed.