Bug fixes and general improvements
- Pulled in some bug fixes from https://github.com/MarkDShattuck/Clockit
- Removed NORMAL_TIME/DEBUG_TIME
- Changed all #defines to use uppercase
- Remove true/false defines
- Added struct to hold times
- Added enum form maximum unit
- Added half_siren
- Countdown working properly
- Moved display_time logic to timer2
- Start/stop buttown working