Console WIP: Implement lowest-level logicfor cursor manipulation.

Design document for Console output

Update man pages

Alter SystemForth and boot code to use new I/O location

Remove mirror logic

Mirror emulator I/O space so we can test incrementally

Refactor address decode logic.

This patch should make it easier to relocate emulator I/O to any
arbitrary location in the 65816's address space.

Fix KIA->KIA-II emulation, update docs

Introduce memory accessors for 16MB address space

Reuse Oberon-07 PS/2 encoder with attribution

Integrate CPU-side interface of KIA

Refactor

Test full queue behavior

Test pushing multiple bytes into queue

Refactor; code hygiene

Test pushing a byte to an empty KIA queue

test popping an empty KIA queue

cargo fmt

Support opening the root directory

This code should technically work with any directory.  However, we don't
implement Twalk yet.

General clean-up tasks

Implement Tauth by letting default not-implemented behavior resolve it.
Rename FSObject trait to OpenFileHandlers, since FSObject makes more
sense as a struct.