Improve interrupt handling

[Ruin0x11]

• Replaces the main interrupt handler with a new "switchboard" design that dispatches based on interrupt kind, mostly inspired by tonclib.
• Allow setting an individual interrupt handler function per interrupt kind.
• Add some convenience functions for enabling/disabling the triggering of each interrupt.
• Add documentation about the interrupt handling features.

Closes #152. Closes #127.

[Hpmason]

While we're adding better IRQ handling, would it be a good idea to work on #150? The examples seem to be the only problem in the CI. I was able to build the examples by adding the new IRQ handling to the examples.

[Lokathor]

sounds reasonable.

[Lokathor]

This is now very stale, I'll close it.