* Introduce the URIBeacon2 service.
* Add helper API Gap::MSEC_TO_ADVERTISEMENT_DURATION_UNITS(); this can then be
used in calls to setAdvertisingInterval().
* Remove Stream as a base class for UARTService. Instantiating Stream() was
causing the C library to initialize the serial console UART implicitly;
which caused a constant drain of around 1mA. This change means that we can
no longer benefit from the APIs offered by Stream, and we can no longer re-
target STDOUT to UARTService like before; but that's not worth losing 1mA.
* Remove some un-necessary header files from BLEDevice.h.
This release is backward compatible with 0.2.4.