Fix servo not working on ESP32-S2

[brentru]

Addresses #313

• Drops LEDC timer resolution for a servo to 12 bits,
• Noting, while ESP32x can go up to a 16-bit timer width, ESP32-S2 does not work properly at this resolution. So, for the purposes of keeping this library compatible with multiple ESP32x platforms, the timer width has been scaled down to 12 bits and the calculation for the duty cycle was adjusted accordingly.
• Adds optional resolution parameter to attachPin() call in LEDC manager.
• Removes hardcoding within the writeMicroseconds count formula to accept a variable (#define'd) timer resolution.

Tested on:
Adafruit ESP32 Feather V2
Adafruit QT Py ESP32-S2