scratch like broadcast api (#1358)

* scratch like broadcast api

* always register handler

* adding docs

* added icon

* updated block name

* adding DAL support "radio.raiseEvent"

* typo

* implemented using radiobus

* adding docs

* adding raise event block

* updated shims

* updated pxt

docs/reference/radio/raise-event.md

@@ -0,0 +1,14 @@
+# Raise Event
+
+Sends an event over radio to be raised in the event bus of other @boardname@. 
+
+```sig
+radio.raiseEvent(control.eventSourceId(EventBusSource.MICROBIT_ID_BUTTON_A), control.eventValueId(EventBusValue.MICROBIT_EVT_ANY));
+```
+
+**This is an advanced API.**  For more information, see the
+[@boardname@ runtime messageBus documentation](https://lancaster-university.github.io/microbit-docs/ubit/messageBus/)
+
+## See Also
+
+[control raise event](/reference/control/raise-event)