Performance enhancements in IODevice::loop() function.
Improved error handling, device is placed off line if not responding.
Improved error reporting, device shown as offline if not operational (faulty or not present).
When writing to analogue outputs pins, the digital _read() function now returns the 'busy' status of the analogue pin. Consequently, the _isBusy() function becomes superfluous and has been removed. The static IODevice::isBusy() function now calls the object's _read() function instead.
Also, limit in DFPlayer of 3 pins has been removed.
When writing to a PWM device (servo or LED for example), it is possible to request the target position in the call, or to ask for a SET or RESET position. In the latter case, the positions corresponding to SET and RESET must be known, i.e. preconfigured. Defaults were assigned for this, but because the correct values will depend on the hardware device being driven, the defaults have been removed.
In addition, the <T> command, when defining a servo turnout, now configures the PWM positions (not required by <T> commands, but desirable for consistency with other commands).
IODevice::writeAnalogue() has an additional optional parameter "duration", specifying the time taken for the animation in units of 100ms (max 3276 seconds, or about 54 minutes).
* Add <D SERVO vpin position> command
Allow a PWM servo to be driven to any arbitrary position.
* Enhancements for HAL drivers
Add state change notification for external GPIO module drivers;
Allow drivers to be installed statically by declaration (as an alternative to the 'create' call).
* Create IO_HCSR04.h
HAL driver for HC-SR04 ultrasonic distance sensor (sonar).
* Enable servo commands in NO-HAL mode, but return error.
Avoid compile errors in RMFT.cpp when compiled with basic HAL by including the Turnout::createServo function as a stub that returns NULL.
* Update IO_HCSR04.h
Minor changes
* Change <D SERVO>
Give the <D SERVO> command an optional parameter of the profile. For example, <D SERVO 100 200 3> will slowly move the servo on pin 100 to PWM position corresponding to 200. If omitted, the servo will move immediately (no animation).
* IODevice (HAL) changes
1) Put new devices on the end of the chain instead of the beginning. This will give better performance for devices created first (ArduinoPins and extender GPIO devices, typically).
2) Remove unused functions.
* Update IO_HCSR04.h
Allow thresholds for ON and OFF to be separately configured at creation.
* Update IODevice.cpp
Fix compile error on IO_NO_HAL minimal HAL version.
* Update IO_PCA9685.cpp
Remove unnecessary duplicated call to min() function.
