v0.3.0

This version of Strike adds keyboard shortcuts for undo and redo (using Ctrl-Z  for undo and Ctrl-Y or Ctrl-Shift-Z for redo), which should work on all major operating systems -- though I have not personally tested it on Mac. Please let me know either here or on Github if you run into any problems.

I might eventually adding keyboard shortcuts for the other tools too, but I'm not quite sure what format to make them yet. (The only shortcuts I use normally are undo and redo, hence why they went in first.) As mentioned before, I don't have any formal plans or roadmap for future features, but if anyone has any ideas or opinions, I'd be happy to hear them.