Added Functionality to manually set the integral term.

[padalev]

This might be important to set controller to previous state after an interruption or crash. It also allows for more manual manipulation of the PID controller if that is desired.
I have added a function set_integral_term() which is very similar to reset_integral_term() but takes the desired value as a parameter.
I have left the original reset_integral_term() in the code even though this kinda doubles functionality to not break behaviour that might be expected by people that have used the reset_integral_term() before.

[SwenBischof]

Hi @braincore this pull request would actually be very interesting for battery powered devices. So that the integral term can be restored after for example a deep sleep.

[braincore]

@SwenBischof That makes plenty of sense.

@padalev Sorry for the delay. Can we drop the dt changes and instead only add set_integral_term()? @SwenBischof Feel free to submit another PR if you can't wait.

[padalev]

Sure. I'm not insisting on anything here. I still believe it would make sense to properly implement dt as this is really a key part of a proper PID implementation but that's obviously not the point of this PR. So let's just drop that for now and just do the integral term part right now.

[SwenBischof]

@padalev Sorry for the delay. Can we drop the dt changes and instead only add set_integral_term()? @SwenBischof Feel free to submit another PR if you can't wait.

I am mainly interested in the manual setting of the integral term. I think for that reason it doesn't make sense to create another pull request..

[mtilda]

Since I am not able to push to this branch, I created a new branch and PR (#27) with 3ae1fe5. Happy to close my PR as a duplicate if this one is updated.