support for buffer signature (#325)

docs/reference/bluetooth/advertise-uid-buffer.md

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+# Avertise UID Buffer
+
+Advertises a UID via the Eddystone protocol over Bluetooth.
+
+## ~hint
+
+### Eddystone
+
+Bluetooth beacons are used to indicate proximity to a place or object of interest. 
+Beacons use Bluetooth advertising to broadcast a small amount of data, 
+which can be received and acted upon by anyone in range with a suitable device and software, typically a smartphone and application.
+
+There are various beacon message formats, which define the way Bluetooth advertising packets are used as containers for beacon data. 
+iBeacon is Apple's beacon message format. Eddystone comes from Google.
+
+Read more at https://lancaster-university.github.io/microbit-docs/ble/eddystone/ .
+
+## ~
+
+```sig
+bluetooth.advertiseUidBuffer(pins.createBuffer(16), 7, true);
+```
+
+### Parameters
+
+* ``buffer`` - a 16 bytes buffer containing the namespace (first 10 bytes) and instance (last 6 bytes).
+* ``power`` - a [number](/reference/types/number) representing the power level between 0 (short) and 7 (maximum range).
+* ``connectable`` - a [boolean](/reference/type/boolean) indicating whether or not the micro:bit should accept connections. 
+
+
+## See Also
+
+[stop-advertising](/reference/bluetooth/stop-advertising), [advertise-uid](/reference/bluetooth/advertise-uid)
+
+```package
+bluetooth
+```