The `web-standalone` target does what the old `web` target did: Produce
the WASM, JS, and an index.html so the output can be served up directly.
The new `web` target renames the "index.html" to "boids.html" so it can
be used as a submodule/subpage in a larger website build.
Variables that a package consumer might want to adjust should be placed
at the top of the file so they are immediately visible. Any constants
shall live below those (just the SRC folder, really).
I had named it makefile_web" in an effort to communicate to the user
that the Make-based build path is only for web builds. It's annoying to
type all that out, though, and it doesn't seem like other projects
follow this convention. I'll just put a usage note at the top. It's not
like the Makefile can be mis-used to make a non-web version. There is no
footgun here.
