webstead: use .mjs for JavaSript module

This means that emcc automatically uses the correct mode, and seems
slightly more correct to me.

Makefile

@@ -21,7 +21,7 @@ all: $(DISTFILES)
 
 .PHONY: all-web
 all-web: all sample.png extended.png icon-16.png icon-32.png icon-64.png \
-	bedstead.js
+	bedstead.mjs
 
 .PHONY: experimental
 experimental: bedstead-chiseltip.otf bedstead-plotter-thin.otf \
@@ -112,15 +112,15 @@ bedstead-complement.ps: bedstead
 bedstead-complement.pdf: bedstead-complement.ps bedstead.otf Fontmap
 	ps2pdf -P $< $@
 
-EMCCFLAGS = -O2 -sEXPORT_ES6 -sEXIT_RUNTIME -sSTRICT \
+EMCCFLAGS = -O2 -sEXIT_RUNTIME -sSTRICT \
 	-sINCOMING_MODULE_JS_API='["arguments","print"]'
 EMCCFLAGS += $(CWARNFLAGS)
-%.js: %.c
+%.mjs: %.c
 	emcc $(EMCCFLAGS) -o $@ $<
 
 .PHONY: clean
 clean:
-	rm -f bedstead *.ttx *.otf *.bdf *.bdf.ps *.png *.pdf *.js *.wasm \
+	rm -f bedstead *.ttx *.otf *.bdf *.bdf.ps *.png *.pdf *.mjs *.wasm \
 		bedstead-complement.ps
 
 .PHONY: install-user

webstead.xhtml

@@ -147,7 +147,7 @@
         document.querySelector('#drawing').onclick = drawing_click;
         update_glyph(true);
     }
-    import("./bedstead.js").then((module) => {
+    import("./bedstead.mjs").then((module) => {
         Bedstead = module.default;
         // This script is loaded asynchronously, so make sure the DOM is
         // loaded before touching it.