added radio transmit power

sim/libmbit.ts

@@ -445,6 +445,9 @@ namespace ks.rt.micro_bit {
         board().radio.setGroup(id);
     }
     
+    export function setTransmitPower(power: number) : void {
+        board().radio.setTransmitPower(power);           
+    }
 
     export function datagramSendNumbers(value0 : number, value1: number, value2: number, value3: number) : void {
         board().radio.datagram.send([value0, value1, value2, value3]);