eventbus: make it usable and add README

examples/eventbus/.gitignore

@@ -0,0 +1 @@
+eventbus

examples/eventbus/eventbus.v

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+module main
+
+import (
+	some_module
+	eventbus
+)
+
+fn main(){
+	mut sub := some_module.get_subscriber()
+	sub.subscribe("error", on_error)
+	some_module.do_work()
+}
+
+fn on_error(p eventbus.Params) {
+	println(p.get_string("error"))
+}

examples/eventbus/some_module/some_module.v

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+module some_module
+
+import (
+	eventbus
+)
+
+const (
+	eb = eventbus.new()
+)
+
+pub fn do_work(){
+	mut params := eventbus.Params{}
+	for i in 0..20 {
+		println("working...")
+		if i == 15 {
+			params.put_string("error", "CRASH!!")
+			eb.publish("error", params)
+			eb.publish("error", params)
+			return
+		}
+	}
+	
+}
+
+pub fn get_subscriber() eventbus.Subscriber {
+	return eb.subscriber
+}