[notready] streams for copying

Implements read/write streams for copying. This is unfortunately a bit more complex than needs to be for good performance as the node stream API assumes ordered data and thus makes concurrent get/put tile handling up to the implementer to do behind the scenes.

Not ready yet.

- [ ] update copy command, add tests copy command
- [ ] branch of tm2 for some real live testing of performance
- [ ] more tests for mem usage/concurrency esp of pyramid stream
- [ ] concurrency as option