Bugfix WebRTCBin.createOffer/createAnswer; Support for WebRTC DataChannel (string/data)

[jw-tecuri]

Fixes #270

[svnhub]

Quite useful changes! - especially the garbage collection of promises are really important. Maybe other parts of the codebase actually has the same/similar issue?

Suggestion: Add offset+length versions of the GBytes and datachannel data methods for effeciency reasons, to avoid having to copy over byte arrays in situations where only a portion needs to be used (very common). Maybe something along the lines of:

WebRTCDataChannel:

    /**
     * Sends a sub-section of binary data through this {@link WebRTCDataChannel}.
     *
     * @param bytes  The source array.
     * @param offset The starting position in the source array.
     * @param length The number of bytes to send.
     */
    public void sendMessage(byte[] bytes, int offset, int length) {
        GBytes gbytes = GBytes.createInstance(bytes, offset, length);
        gbytes.disown();

        emit("send-data", gbytes);
    }

    /**
     * Sends binary data through this {@link WebRTCDataChannel} which will be received by connected remote peers.
     * * @param bytes that should be sent over the WebRTC data-channel connection.
     */
    public void sendMessage(byte[] bytes) {
        sendMessage(bytes, 0, bytes.length);
    }    

GBytes:

    /**
     * Creates a GBytes instance from a sub-section of a byte array.
     * @param bytes  The source array.
     * @param offset The starting position in the source array.
     * @param length The number of bytes to copy.
     * @return A new GBytes instance.
     */
    public static GBytes createInstance(byte[] bytes, int offset, int length) {
        // Allocate native memory specifically for the 'length' we want to copy
        Pointer source = new Memory(length);

        // write(long peerOffset, byte[] buf, int arrayOffset, int len)
        source.write(0, bytes, offset, length);

        Pointer ptr = GLIB_API.g_bytes_new(source, length);

        return new GBytes(new Handle(new GPointer(ptr), true));
    }

    /**
     * Creates a GBytes instance from the full byte array.
     */
    public static GBytes createInstance(byte[] bytes) {
        return createInstance(bytes, 0, bytes.length);
    }