First commit of RSSI proximity project

Author: microbuilder

libraries/Bluefruit52Lib/examples/Projects/rssi_proximity/README.md

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+# RSSI Proximity Project
+
+This project demonstrates how you can use a single Bluefruit nRF52 device
+running in Central mode to listen for a specific signature in the advertising
+packets of nearby Bluefruit nRF52 devices running in peripheral mode.
+
+The Central mode device will sort those devices with the matching signature by
+proximity based on their RSSI (relative signal strength) value.
+
+Most of the Central mode advertising API is used in this demo, making it an
+excellent place to start if you want to create your own custom Central based
+project(s).
+
+## Project Files
+
+This project consists of two parts:
+
+- `rssi_proximity_central`: This project should be run on one Bluefruit nRF52
+  board and will configure the board as a Central device, actively scanning
+  for any peripheral devices in listening range.
+- `rssi_proximity_peripheral`: This project should be run on one or more
+  Bluefruit nRF52 boards and will configure the boards as peripheral devices,
+  sending out a specifically formatted advertising packet at a regular
+  interval.