TODO:

- download ROM file
- NaN in cycle count for macros
- debugging of scan line overflow
- confuse code/data in listing
- show memory locations hovering over lines
- don't play sound when debugging
- coalesce compile events
- don't check against ROM signatures
- better errors when ROM format wrong
- debugging inside of bank switching??? relocated segs?
- support 6502 test cases
- DASM: macro forward refs
- support narrow screens
- show other TIA internal values
- case sensisitvity looking for mismatch variables
- remove pulldown when no preset?
- some units test maybe
- can't step after reset (or when funky frame; TIA frame is out of sync)
- break on BRK/illegal opcode?