Update CHANGELOG and Documentation

I've added all changes since 1.15 to the changelog, except all the BLE stuff. I'm not too sure what all the things were that have changed, so @schneider, if you can give me a rough list, I'll integrate them here as well.

CHANGELOG.md

@@ -8,13 +8,25 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - `leds.flash_rocket()` API for making rockets flash asynchronously.
 - Basic API for the MAX86150 pulse-oximeter.
 - A feature to allow setting the main app on-device.
+- Added compatibility to BLE 5.0 capable phones (including iPhones).
+- Added pairing dialog in BLE app. Device is only visible when BLE app is
+  active.
+- Option to write HCI layer log files for debugging.
+- _Stub_ `ubluetooth` module.  Not yet functional!
+
 
 ### Changed
 - Internal changes to the way interrupts are triggered.
 - Updated to a newer version of MicryPython (v1.12).
+- Improved BLE security by only allowing man-in-the-middle protected
+  pairings and specifying minimum key lengths.
 
 ### Fixed
 - Made the `vibra` vibration motor API more stable.
+- Fixed bug which triggered reboot loops.
+- Fixed bug which made the USB serial connection unresponsive.
+- Fixed bug which wrote the pairings file more periodically.
+- Fixed invalid filesystem locking in BLE startup.
 
 
 ## [v1.15] - 2020-02-02 - [Okra]