Big addition is job01::mem::blocks.  This is based on and supercedes the
recently-added job01::core::pool.  See documentation and examples in blocks.h
and test_blocks.cc.

Fix bugs in job01::core::queue to work with the recently-added support for
generic pointer types in link.h.

TODO: investigate adding unit-tests demonstrating these bugs.

Fix bugs due to Link/Linker moving into job01::core...
guess I haven't been running all tests for a while ?!?

job_pool.h is busted, again for who knows how long?  Just comment it out...
it will be rewritten soon anyway.
Refining BlockArray API.
Split blocks.h into a second "impl" file/namespace.
Rename classes so that public versions are more concise.