Fix typos

The "codespell" spellchecker tool is used to automatically detect commonly misspelled words in the files of this
project.

The misspelled words dictionary was expanded in recent releases of codespell, which resulted in the detection of
misspelled words in the project files:

> Error: ./src/utility/HCI.cpp:761: Signalling ==> Signaling
> Error: ./docs/readme.md:22: acknowledgement ==> acknowledgment

The typos are hereby corrected, which will restore the spell check to a passing state.

---

I supplemented the correction of the automatically detected typos with a general review of the project content,
fixing the additional typos I identified during that review.

CHANGELOG

@@ -2,7 +2,7 @@ ArduinoBLE ?.?.? - ????.??.??
 
 ArduinoBLE 1.1.2 - 2019.11.12
 
-* cordio: switch to lower power when polling with timeout 
+* cordio: switch to lower power when polling with timeout
 * Fixed issue with wrong types for disconnection event handling. Thanks @cparata
 
 ArduinoBLE 1.1.1 - 2019.09.05

README.md

@@ -2,11 +2,11 @@
 
 [![Compile Examples Status](https://github.com/arduino-libraries/ArduinoBLE/workflows/Compile%20Examples/badge.svg)](https://github.com/arduino-libraries/ArduinoBLE/actions?workflow=Compile+Examples) [![Spell Check Status](https://github.com/arduino-libraries/ArduinoBLE/workflows/Spell%20Check/badge.svg)](https://github.com/arduino-libraries/ArduinoBLE/actions?workflow=Spell+Check)
 
-Enables Bluetooth® Low Energy connectivity on the Arduino MKR WiFi 1010, Arduino UNO WiFi Rev.2, Arduino Nano 33 IoT, Arduino Nano 33 BLE, Arduino Portenta H7, Arduino Giga R1 and Arduino UNO R4 WiFi.
+Enables Bluetooth® Low Energy connectivity on the Arduino MKR WiFi 1010, Arduino UNO WiFi Rev2, Arduino Nano 33 IoT, Arduino Nano 33 BLE, Arduino Portenta H7, Arduino Giga R1 and Arduino UNO R4 WiFi.
 
 This library supports creating a Bluetooth® Low Energy peripheral & central mode.
 
-For the Arduino MKR WiFi 1010, Arduino UNO WiFi Rev.2, and Arduino Nano 33 IoT boards, it requires the NINA module to be running [Arduino NINA-W102 firmware](https://github.com/arduino/nina-fw) v1.2.0 or later.
+For the Arduino MKR WiFi 1010, Arduino UNO WiFi Rev2, and Arduino Nano 33 IoT boards, it requires the NINA module to be running [Arduino NINA-W102 firmware](https://github.com/arduino/nina-fw) v1.2.0 or later.
 
 For the Arduino UNO R4 WiFi, it requires the ESP32-S3 module to be running [firmware](https://github.com/arduino/uno-r4-wifi-usb-bridge) v0.2.0 or later.