Add a Makefile to automate the web build proc

This is also copied from my Boids project, just like the HTML page was.

.gitignore

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

Makefile

@@ -0,0 +1,46 @@
+##
+## This Makefile exists to produce WASM builds.
+## Do not use it if that isn't your goal!
+##
+
+SRC_DIR = ./src
+SRCS := $(wildcard $(SRC_DIR)/**)
+
+# Patch these to select a different build profile or target
+# The target shouldn't change any time soon. WASM64, I guess. Other targets
+# aren't aimed at the web, so you shouldn't be using this makefile.
+CARGO_TARGET := wasm32-unknown-unknown
+CARGO_PROFILE := tiny
+
+.PHONY: clean full-clean web tarball
+
+web: out/asteroids.js out/asteroids_bg.wasm out/index.html
+
+tarball: asteroids_web_root.tar
+
+asteroids_web_root.tar: out/asteroids.js out/asteroids_bg.wasm out/index.html
+	tar -caf $@ $^
+
+target/$(CARGO_TARGET)/$(CARGO_PROFILE)/asteroids.wasm: $(SRCS) Cargo.lock Cargo.toml
+	cargo build --profile $(CARGO_PROFILE) --target $(CARGO_TARGET)
+
+out:
+	mkdir $@
+
+# Both the JS and WASM files are generated by the wasm-bindgen call, so both
+# get to be on the target half of this recipe.
+out/asteroids.js out/asteroids_bg.wasm &: target/$(CARGO_TARGET)/$(CARGO_PROFILE)/asteroids.wasm | out
+	wasm-bindgen --no-typescript --target web --out-dir ./out/ --out-name asteroids target/$(CARGO_TARGET)/$(CARGO_PROFILE)/asteroids.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/ asteroids_web_root.tar
+
+# Delete everything, including the Cargo build cache. In case someone needs
+# this, I guess.
+full-clean: clean
+	cargo clean