xP: use the binary protocol for incoming events

And batch event messages together as much as possible.

JSON has proven itself to be really slow
(for example, encoding/json.Marshaler is a slow interface),
and browsers have significant overhead per WS message.

Commands are still sent as JSON, sending them in binary
would be a laborious rewrite without measurable merits.

The xP server now only prints debug output when requested,
because that was another source of major slowdowns.

xP/Makefile

@@ -1,13 +1,15 @@
 .POSIX:
 .SUFFIXES:
 
-outputs = xP proto.go public/mithril.js
+outputs = xP proto.go public/proto.js public/mithril.js
 all: $(outputs)
 
 xP: xP.go proto.go
 	go build -o $@
 proto.go: ../xC-gen-proto.awk ../xC-gen-proto-go.awk ../xC-proto
 	awk -f ../xC-gen-proto.awk -f ../xC-gen-proto-go.awk ../xC-proto > $@
+public/proto.js: ../xC-gen-proto.awk ../xC-gen-proto-js.awk ../xC-proto
+	awk -f ../xC-gen-proto.awk -f ../xC-gen-proto-js.awk ../xC-proto > $@
 public/mithril.js:
 	curl -Lo $@ https://unpkg.com/mithril/mithril.js
 clean: