Serial events (#337)

* added "serial->on data received"

* updated info

* updated docs

* added readline to read entire buffer

* lazy initialize of serial buffers

* init async on event

* updated docs

sim/state/serial.ts

@@ -35,18 +35,14 @@ namespace pxsim.serial {
         board().writeSerial(s);
     }
 
+    export function readUntil(del: string): string {
+        return readString();
+    }
+
     export function readString(): string {
         return board().serialState.readSerial();
     }
 
-    export function readLine(): string {
-        return board().serialState.readSerial();
-    }
-
-    export function readUntil(del: string): string {
-        return readLine();
-    }
-
     export function onDataReceived(delimiters: string, handler: RefAction) {
         let b = board();
         b.bus.listen(DAL.MICROBIT_ID_SERIAL, DAL.MICROBIT_SERIAL_EVT_DELIM_MATCH, handler);