Refactored keyboard event I/O code into PKPowerKeyEventListener
 - Moved preferences window code into PKPreferencesController
 - Misc. cleanup and changes
 - Renamed `kPowerKeyUserPrefKey` to `kPowerKeyReplacementKeycodeKey`
- If app is NOT set to open at login, always show prefs on launch.
 - If prefs window is open when app is terminated, show window when app is run again
 - If prefs window is closed, do not show window when app is run again.
 - This should mostly fix #4
 - It would be better to determine if app definitely was "launched at login" and not by user… not sure if that's possible. (+1 squashed commit)
Squashed commits:
[4b1dd81] - If app is NOT set to open at login, always show prefs on launch.
 - If prefs window is open when app is terminated, show window when app is run again
 - If prefs window is closed, do not show window when app is run again.
 - This should mostly fix #4
 - It would be better to determine if app definitely was "launched at login" and not by user… not sure if that's possible. (+1 squashed commit)
Squashed commits:
[c3dfa12]  - If app is NOT set to open at login, always show prefs on launch.
 - If prefs window is open when app is terminated, show window when app is run again
 - If prefs window is closed, do not show window when app is run again.
 - This should mostly fix #4
 - It would be better to determine if app definitely was "launched at login" and not by user… not sure if that's possible.
 - Removed unsafe release of eventTap
 #5
 - Limiting event monitoring mask to a subset of events
 - Can't only monitor `NSSystemDefined` events; produces bugs for events in certain other apps.
 - #5
 - Now ignoring NSEventTypeRotate events
 - Switched to using a switch
 - Fixes #5
 -  Allowing modifier keys + power key for all modifier keys except Fn
 - Switched behavior of the two power key system events. The first event is now replaced and the second event is killed.
 - Fixes #9; PowerKey now works well with Command and Control
Revved to version 1.1
Cleanup
 - Added `F13` as a power key replacement option
 - Set Powerkey to use F13. Then set your favorite app to perform a special function when F13 is pressed.
 - Fixes #7