Merge Devel-nmck:
I2C Multiplexer support through Extended Addresses added for Wire, 4209 and AVR I2C drivers.
I2C retries when an operation fails.
I2C timeout handling and recovery completed.
I2C SAMD Driver Read code completed.
PCF8575 I2C GPIO driver added.
EX-RAIL ANOUT function for triggering analogue HAL drivers (e.g. analogue outputs, DFPlayer, PWM).
EX-RAIL SCREEN function for writing to screens other than the primary one.
Installable HALDisplay Driver, with support for multiple displays.
Layered HAL Drivers PCA9685pwm and Servo added for native PWM on PCA9685 module and for animations of servo movement via PCA9685pwm. This is intended to support EXIOExpander and also replace the existing PCA9685 driver.
Add <D HAL RESET> to reinitialise failed drivers (it calls the _begin method of all HAL drivers to reinitialise them).
Add UserAddin facility to allow a user-written C++ function to be declared in myHal.cpp, to be called at a user-specified frequency.
Add ability to configure clock speed of PCA9685 drivers (to allow flicker-free LED control).
Improve stability of VL53L0X driver when XSHUT pin connected.
Enable DCC high accuracy mode for STM32 on standard motor shield (pins D12/D13).
Incorporate improvements to ADC scanning performance (courtesy of HABA).
Enable hardware pulse generation on STM32 for pins 12 and 13 (standard motor shield pins), using timers TIM2 and TIM3. Any other pins will currently be controlled directly by the interrupt routine (in effect, by digitalWrite calls).
UserAddin allows a function to be 'plugged in' to the IODevice (HAL) framework and executed cyclically, using just one line of code in the myHal.cpp. This will facilitate functions for displaying CS state on OLEDs and LCDs, among other things.
If an extended I2C address is specified (including mux and/or subbus) then these parameters are ignored, but a warning output to the diagnostic console.
Report address 0x3d as (probably) OLED Display.
If an I2C probe for a device times out, assume that there's a bus problem on the MUX sub-bus, and skip the rest of the devices on that bus. This reduces the impact of the long timeout on some Wire implementations.
