Fix attach servo with initial value

[om2804]

functions

uint8_t attach(int pin);
uint8_t attach(int pin, uint16_t min, uint16_t max);

always sets 0 (zero) as the initial value. This is not obvious. It does not allow to attach servo without movement.

I changed the body of functions, so that the movement was caused only when transmitting the value to the function.
uint8_t attach(int pin, uint16_t min, uint16_t max, int value);

[dok-net]

What is wrong with using this overload, as it is intended to serve your use case:

    // attach the given pin to the next free channel, sets pinMode, min, and max values for write(),
    // and sets the initial value, the same as write().
    // returns channel number or 0 if failure.
    uint8_t attach(int pin, uint16_t min, uint16_t max, int value);

[om2804]

@dok-net In the current implementation, it is impossible attach without moving a servo drive. This is not obvious. This violates compatibility with https://github.com/arduino-libraries/servo.

[dok-net]

[...] violates compatibility with https://github.com/arduino-libraries/servo.

I have checked the implementations for AVR and and SAMD in that lib. The Servo constructor sets a default position, attach starts the PWM on the set pin. To be sure, write does nothing more but update the position. I can't see how your claim that in that library attach would not cause the servo to move unless it is the default position to begin with already.

[om2804]

Moving to zero will be at each attach after deattach without a reconstruction of a class instance.

example:
servo = new Servo();
servo .attach(9); // move to 0, first attach, it's ok
servo.write(value); // move to value
servo.detach();
servo.attach(9); // current implementation moves servo to 0, it's not ok
servo.write(value); // move to value

[dok-net]

@om2804 No offense, but I am certain I have a simpler solution that does what you requested. Please review.

[om2804]

@ dok-net ok. I close this PR.