* Add RGBA color blending support in WASM build.
* Initial texture caching API for Canvas renderer engine. The WASM build
writes the chunk caches as a "data:image/png" base64 URL on the
browser's sessionStorage, for access to copy into the Canvas.
* Separated the ClickEvent from the MouseEvent (motion) in the WASM
event queue system, to allow clicking and dragging.
* Added the EscapeKey handler, which will abruptly terminate the WASM
application, same as it kills the window in the desktop build.
* Optimization fix: I discovered that if the user clicks and holds over
a single pixel when drawing a level, repeated Set() operations were
firing meaning multiple cache invalidations. Not noticeable on PC but
on WebAssembly it crippled the browser. Now if the cursor isn't moving
it doesn't do anything.
* Refactor the event system in the WASM render engine to serialize the
async JavaScript events into a channel, so that queued events are read
off serially in the main loop similar to SDL. This fixes keyboard
input issues, altho if you type really fast some input keys get lost.
* Add a Red Azulian as a test for mobile enemies.
* Its A.I. has it walk back and forth, changing directions when it
comes up against an obstacle for a few moments.
* It plays walking animations and can trigger collision events with
other Doodads, such as the Electric Door and Trapdoor.
* Move Gravity responsibility to the doodad scripts themselves.
* Call `Self.SetGravity(true)` to opt the Doodad in to gravity.
* The canvas.Loop() adds gravity to any doodad that has it enabled.
* Add some encoding/decoding functions for binary msgpack format for
levels and doodads. Currently it writes msgpack files that can be
decoded and printed by Python (mp2json.py) but it can't re-read from
the binary format. For now, levels will continue to write in JSON
format.
* Add filesystem abstraction functions to the balance/ package to search
multiple paths to find Levels and Doodads, to make way for
system-level doodads.
