Tophat downloads

• Complete rewrite of the rendering and platform backend
• add web export support
• add th.Quad.getDims
• change the mainloop structure

Built automatically from the `main` branch on every push. It contains the newest features, but main contain bugs and unannounced API changes.

This is the latest release.

• signal.um rework
• anim.um rework
• add nav.um
• add canvas.drawQuad
• windows build support (by ~ske)
• window utility functions