Abstract memory (#283)

* Add Access Memory abstract command

Source provided by Thomas Wicki

* Add autoincrement to abstract memory access

Also added examples in the debugger implementation section.

* Thomas requested Robert get credit for this idea.

* Incorporate review back, add aamvirtual bit

Removed transfer and postexecute bits from abstract memory access.
Renamed a few fields to avoid confusion.
Add aamvirtual bit to abstract memory access.

* Fix memory references to include abstract command

* Fix typo.