See #57 (comment)
The result seems to be more or less identical to the one obtained with
sphbesselh_zeros() in terms of stability -- the obtained values for z, p differ
quite a lot.
One advantage of sphhankel_laplace() is that it will not lead to Inf or Nan, but
only to large numerical errors in the reproduced sound field for orders >85.

Maybe it would be a good idea to try to calculate z directly via an formula
without using the zeros() function.

The poles are always zero and are now directly set by zeros()

The function has now a hardcoded method switch to choose between both methods
for calculatinh the zeros. We should do some testing which is the better method
and use that one.