Xbee 802.15.4 modem driver for Arduino

[rousselk]

This radio driver allows to use an XBee 802.15.4 modem with an Arduino board, using the official Arduino Wireless/SD shield (see http://arduino.cc/en/Main/ArduinoWirelessShield) for connection.

Follow-up to #1463 (from my new personal repository).

[rousselk]

Todo (to remove the WIP status): make this code conformant to the new network API defined in #1492.

I will do it as soon as I have time...

[haukepetersen]

Looking good on first sight! I would suggest you wait a week or two with the adaption of the netdev interface, as this is subject to change right now. Would that be ok with you?

[LudwigKnuepfer]

I've just been thinking if it makes sense to have a WITH_XBEE_SHIELD flag the board could use to include the configuration... @Kijewski any thoughts?

[LudwigKnuepfer]

Please split the commit (into drivers:xbee, boards:arduino).

[LudwigKnuepfer]

Have a look at Makefile.dep

124 ifneq (,$(filter defaulttransceiver,$(USEMODULE)))
125     FEATURES_REQUIRED += transceiver
126 endif

Something along this line (for UART instead of transceiver) is useful for this driver as well, right?

[miri64]

#2695 already introduced this feature. If you like to update that implementation please open a new PR.