Basic CoAP library for arduino.
Communication uses WiFiUDP but can easily be changed to any packed based transport.

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* This branch is working as an implementation of the June 2014 version of the CoAP protocol.
* Implements OBSERVE IETF draft (16): https://tools.ietf.org/html/draft-ietf-core-observe
* Block transfer not implemented
*
* Current code has been tested and working on Arduino Mega 2560
*
* Tested against Node-RED v0.10.6 with the node-red-contrib-coap package
*
* Tested functionality:
* GET coap://192.168.0.10/.well-known/core, text/plain
* GET coap://192.168.0.10/light, text/plain
* GET coap://192.168.0.10/button, text/plain, OBSERVE
* POST coap://192.168.0.10/led, text/plain
*
* Not fully tested
   - everything else, e.g. uri queries
* Current TODO list:
   - Make retransmit and observe arrays of vector type
   - Reduce code size
   - Implement random factor for retransmit interval
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/********************************************************************************
 ** The Arduino-CoAP is free software: you can redistribute it and/or modify   **
 ** it under the terms of the GNU Lesser General Public License as             **
 ** published by the Free Software Foundation, either version 3 of the         **
 ** License, or (at your option) any later version.                            **
 **                                                                            **
 ** The Arduino-CoAP is distributed in the hope that it will be useful,        **
 ** but WITHOUT ANY WARRANTY; without even the implied warranty of             **
 ** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the              **
 ** GNU Lesser General Public License for more details.                        **
 **                                                                            **
 ** You should have received a copy of the GNU Lesser General Public           **
 ** License along with the Arduino-CoAP.                                       **
 ** If not, see <http://www.gnu.org/licenses/>.                                **
 *******************************************************************************/