0.18 - Performance overhaul & a few new features

The main point for this version is a major performance overhaul. 

Tools/actions including working with the selection box, dragging, scrolling, typing, and some other things are now more snappy & responsive thanks to the introduction of buffered visual updates. 

Along similar lines, most things work more responsively when combining the Navigator window with larger canvases, which had a severe CPU scaling problem before. 

Set Canvas size improvements:

Canvas size has been set free. You can now set the canvas dimension to any tile-multiple value by typing directly into the corresponding boxes.
For convenience, buttons for adding/detracting whole screens to the canvas dimensions have been added as well. 

There's more minor fixes too. For a full review, please view the changelog in the zip.