Added describe.setSlowTimeout(...)/describe.restoreSlowTimeout()

- Useful for slow-running acceptance tests, e.g. those testing the ROMBIOS POST boot sequence (or further)
Monkey-patched a trap for interrupts, to allow acceptance tests to hook in when an interrupt is raised
Moved sample acceptance test to be more specific

- Now it is clearer that only NOP is being tested (a simple sanity check)
Added comment for existing monkey-patch
Changed public API to only expose a "CPU state" object
Fixed bug with non-existant .pause() method being called (legacy API uses "halt")
Added ROMBIOS POST acceptance test

- Asserts that the last instruction in the POST is reached, where INT 0x19 is raised - "Boot Load Service Entry Point"