GH-120: Add NFC API

[mattleibow]

DISCLAIMER: I have no iOS device or any official tags. I am testing with an Android-based tag emulator. Things may not work. 😉

Description of Change

Adding the NFC API.

Bugs Fixed

• Related to issue NFC API #120

API Changes

public static partial class Nfc {
    // when a tag comes near
    public static event NfcTagEventHandler TagArrived;
    public static event NfcTagEventHandler TagDeparted;
    public static event NdefMessageReceivedEventHandler NdefMessageReceived;

    // basically enable/disable events
    public static bool IsListening { get; set; }

    // writing (not supported on iOS)
    public static void PublishMessage(string messageType, byte[] message);
    public static void StopPublishing();

    // helpers for writing NDEF tags (uses PublishMessage under the hood)
    public static void WriteTag(byte[] message);
    public static void ShareTag(byte[] message);
}

public delegate void NfcTagEventHandler(NfcTagEventArgs e);

public delegate void NdefMessageReceivedEventHandler(NdefMessageReceivedEventArgs e);

public class NfcTagEventArgs : EventArgs {
    public static new readonly NfcTagEventArgs Empty;
    public NfcTagEventArgs();
}

public class NdefMessageReceivedEventArgs : EventArgs {
    public NdefMessageReceivedEventArgs(byte[] message);
    public byte[] Message { get; }
}

Behavioral Changes

Adding the NFC API.

PR Checklist

• Has tests (if omitted, state reason in description)
• Has samples (if omitted, state reason in description)
• Rebased on top of master at time of PR
• Changes adhere to coding standard
• Updated documentation (see walkthrough)

[mattleibow]

Based on some looking around, if appears that we will leave out writing to tags as this is not easy to do with iOS.

[Redth]

I'm going to close this for now, we can re-open it at a later date.