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

libs/radio-broadcast/radio-broadcast.ts

@@ -0,0 +1,38 @@
+namespace radio {
+    /**
+     * Gets the message code
+     */
+    //% blockHidden=1 shim=ENUM_GET
+    //% blockId=radioMessageCode block="$msg" enumInitialMembers="message1"
+    //% enumName=RadioMessage enumMemberName=msg enumPromptHint="e.g. Start, Stop, Jump..."
+    export function __message(msg: number): number {
+        return msg;
+    }
+
+    /**
+     * Broadcasts a message over radio
+     * @param msg 
+     */
+    //% blockId=radioBroadcastMessage block="radio send $msg"
+    //% msg.shadow=radioMessageCode draggableParameters
+    //% weight=200
+    //% blockGap=8
+    //% help=radio/send-message
+    export function sendMessage(msg: number): void {
+        // 0 is MICROBIT_EVT_ANY, shifting by 1
+        radio.raiseEvent(DAL.MES_BROADCAST_GENERAL_ID, msg + 1);
+    }
+
+    /**
+     * Registers code to run for a particular message
+     * @param msg 
+     * @param handler 
+     */
+    //% blockId=radioOnMessageReceived block="on radio $msg received"
+    //% msg.shadow=radioMessageCode draggableParameters
+    //% weight=199
+    //% help=radio/on-received-message
+    export function onReceivedMessage(msg: number, handler: () => void) {
+        control.onEvent(DAL.MES_BROADCAST_GENERAL_ID, msg + 1, handler);
+    }
+}