Added some fake support for interrupts.

I've added the Interrupt Enabled Flag. Interrupts are not really supported, but some programs that use them will run. That includes the example program from our Computer Architecture classes.

Fixed an important bug

Fixed a bug which sometimes causes the preprocessor to reject valid names for constants and labels.

Fixed an important bug

Fixed a bug that caused the zero flag being sometimes incorrectly set to 0 after shifting right.

Added some visual effects

I've added some visual effects that make it easier to track which registers are used and which are currently changed.

v0.9-beta

The core is, as far as I know, complete right now, but there are probably some bugs left.