This will facilitate the inclusion of extra commands other parts might
want to define.

Replaces individual command parsing. Quite a big and complex chunk of
code, but makes each command much simpler.

Easier to use this way...

They serve a different purpose. The goal of the ACIA buffer is to ensure
that we don't miss an input. The goal of the shell buffer is to wait
until the user presses return.

The ACIA buffer has been moved to shell and replaced with a circular
buffer, a more appropriate data structure for this kind of purpose.

Also, introduce `aciaGetC`.

Also, fix seek reversed endianness.

This introduces `core.asm` which includes routines used by other parts.

This change introduces a command name matching algo.

Also, come up with a way to make parts play well together memory-wise.