antlr4-grammar

When running the regression, the resulting logs seem to end up in third_party/tests/$TEST/.... This of course is not unnoticed by git, so a git status shows a ton of non-added new files added.

To reproduce:

make
make regression
git status   # observe all the files

Build or test artifacts should never clutter the rest of the code-base (we should regard them as read-only in

Currently, when an action is performed (example: drawing a pixel), the action is re-performed when it's initially done and when it's re-done (after being undone).

If someone was to create a big canvas, fill it, then undo it, re-do it, the program might lag, as it's being re-performed every time.

To aid this, an action should be "cache-able", meaning that whatever the action does is saved to