Precision targets for bootstrap functions

[HDembinski]

I worked out how to iterate the permutation tests until a precision target is reached.

It would be great to implement such a functionality also for the functions

• bootstrap.bias
• bootstrap.bias_corrected
• bootstrap.variance
• bootstrap.confidence_interval

This means adding keywords precision and max_size to the functions and to deprecate size (which would act like max_size=size, precision=0). We cannot do this for bootstrap.bootstrap, because we don't know what the user is computing.

With the keyword return_error (default False) we can optionally return the calculated uncertainty in a backward compatible way.