support for buffer packet type (#608)

* support for buffer packet type

* updated description

* updated signature

* added note on json encoding

* adding sendNumbers

* cleanup

* removing 'sendnumbers'

docs/reference/radio/send-buffer.md

@@ -0,0 +1,59 @@
+# Send Buffer
+
+Sends a buffer to other @boardname@s in the area connected by radio. The
+maximum buffer length is 19 bytes.
+
+```sig
+radio.sendBuffer(pins.createBuffer(1))
+```
+
+## Parameters
+
+* `msg` is a [buffer](/types/buffer) to send by radio.
+
+
+## Example: Remote level
+
+If you load this program onto two @boardname@s, each board will send the level information to the other board.
+
+```typescript
+let ax = 0;
+let ay = 0;
+basic.forever(() => {
+    ax = input.acceleration(Dimension.X);
+    ay = input.acceleration(Dimension.Y);
+
+    // encode data in buffer
+    let buf = pins.createBuffer(4)
+    buf.setNumber(NumberFormat.Int16LE, 0, ax)
+    buf.setNumber(NumberFormat.Int16LE, 2, ay)
+    radio.sendBuffer(buf)
+})
+
+radio.onDataPacketReceived(({ receivedBuffer }) => {
+    // decode data from buffer
+    ax = receivedBuffer.getNumber(NumberFormat.Int16LE, 0);
+    ay = receivedBuffer.getNumber(NumberFormat.Int16LE, 2);
+
+    // display
+    basic.clearScreen()
+    led.plot(
+        pins.map(ax, -1023, 1023, 0, 4),
+        pins.map(ay, -1023, 1023, 0, 4)
+    )
+});
+```
+
+## ~hint
+
+A radio that can both transmit and receive is called a _transceiver_.
+
+## ~
+
+## See also
+
+[on data packet received](/reference/radio/on-data-packet-received)
+
+```package
+radio
+```