Big refactor of machine.rs

[omarandlorraine]

There is a mahusive enum that defines all possible operations.

It's inflexible, it's inelegant, it's ugly.

So we're going to break the Operations enum out to variants like ConditionalBranch, DyadicAluOperation, MonadicOperations etc, and these variants will be:

• much more easily randomized and dealt with in the various places.
• lend themselves to use of code deduplication by use of generics
• easier to work with

This work (not strictly a refactor) will also enable the completion of some of the TODOs that there are.

[omarandlorraine]

To get clippy to have less to say, we're going to have to redo the way flags are treated

[omarandlorraine]

We need a test to make sure that an instruction's destination is never immediate.