Updated brush pack (let's call it v1.5?)

Changelog

• Every brush now has a “Delay Correction” setting that does what the “-drift” versions of brushes used to do.
• Brushes now draw when you release the pen, letting you tap in one place and draw (thanks oskkarg!)
• Removed pix-drift.bs and dot2-drift.bs as they’re now obsolete.
• The code for hatch2.bs has been cleaned up somewhat. It’s a little more structured and should be a little more performant than before (it can still be pretty laggy at large sizes since it has to draw several pixels/rectangles individually).