Improve UARTServer example

Improve UARTServer example: now retries after connection dropped.

To use in CircuitPython, simply install the Adafruit CircuitPython bundle.

Read the docs for info on how to use it.

Initial release

Includes:

• LocationBeacon - an iBeacon-style beacon
• EddystoneURLBeacon
• UARTServer - a Peripheral running an implementation of the Nordic UART Service (NUS). Provides a stream interface for reading.

[note - not yet in bundle as of the date of this release, but will be added soon]

To use in CircuitPython, simply install the Adafruit CircuitPython bundle.

Read the docs for info on how to use it.