Setting a default value for adaptive_step

[snilsn]

Another suggestion originating from my work with linking_trackpy():

I think the default value for adaptive_step should be changed from None to 0.95 like in the original trackpy implementation. As long as adaptive_stop is not specified it is not used, but if adaptive_stop is not None, it does make sense to use a reasonable value by default instead of None, because this causes a cryptic exception.

[freemansw1]

I would personally be more inclined to add a more clear error when setting either to None while giving the other a value. I think users should be deliberate when using it, but I am also open to other suggestions!

[snilsn]

That's the other option I had in mind. I guess it involves a bit more coding, but I can totally see your point about using the adaptive search consciously. So I would be happy with adding exceptions if only one of them is None.

[freemansw1]

This has been resolved by #168