Procgen trees - Oak 1st pass

Back again with more incremental tinkering with (or growing of) procedural trees. Having cracked the problem of Y-split shapes in the previous version of my 2D tree generator I have now done an initial rough pass on Oak trees:

First by adding new custom sprites and then creating the specific construction rules to make them actually look more or less like infinite varieties of oak trees. It's starting to look like something, but I need to make more adjustments to get all the pieces to connect properly and allow for the right range of shapes, with enough branches and everything. Will try to add more leaves too, but first I need to get the overall structure right.

Should also do some refactoring and clean up but that's boring so I'll get to that later. Ran into a weird sprite bug in Game Maker that had me going in circles for a while, with one part insisting it had more frames than it should causing all manner of glitches, so I guess I should go and do a report on that.