Add a Makefile to make web builds more ergonomic

Call with `make -f makefile_web` to produce a web root for serving. Use
target "boids_web_root.tar" to bundle the files into a tarball. For...
publishing... or something.

The `wasm-server-runner` program seems to supply it's own index.html and
is doing *something* regarding MIME types -- hosting a dev build of the
Boids program results in the browser complaining about "" (empty string)
being an invalid MIME type.

I want my own index.html during testing, and I can't figure out why the
MIME type info is wrong. I've decided to automate the web-root build
process and serve it up with whatever webserver I have on hand.

.gitignore

@@ -1 +1,2 @@
 /target
+/out

makefile_web

@@ -0,0 +1,32 @@
+.PHONY: clean full-clean web tarball
+
+web: out/boids-sim.js out/boids-sim.wasm out/index.html
+
+tarball: boids_web_root.tar
+
+boids_web_root.tar: out/boids-sim.js out/boids-sim.wasm out/index.html
+	tar -caf $@ $<
+
+target/wasm32-unknown-unknown/wasm-release/another-boids-in-rust.wasm:
+	cargo build --profile wasm-release --target wasm32-unknown-unknown
+
+out:
+	mkdir $@
+
+# Both the JS and WASM files are generated by the wasm-bindgen call, so both
+# get to be on the target half of this recipe.
+out/boids-sim.js out/boids-sim.wasm: out target/wasm32-unknown-unknown/wasm-release/another-boids-in-rust.wasm
+	wasm-bindgen --no-typescript --target web --out-dir ./out --out-name boids-sim.wasm target/wasm32-unknown-unknown/wasm-release/another-boids-in-rust.wasm
+
+out/index.html: www/index.html
+	cp -a $< $@
+
+# Clean the web build, but not the Cargo cache. Cargo handles it's own caching
+# and I don't want to obliterate it all the time.
+clean:
+	rm -rf out/ boids_web_root.tar
+
+# Delete everything, including the Cargo build cache. In case someone needs
+# this, I guess.
+full-clean: clean
+	cargo clean