Deprecate searchsorted(a, v) in util/array.py and replace it with np.searchsorted(a, v, side='right').
(Numba was not supporting the side keyword argument when this function was implemented.)

1. Replace any use of util.array.searchsorted with np.searchsorted(a, v, side='right').
   (⚡️ Speed up function draw by 390% #811 is such an example.)
2. Rewrite searchsorted in util/array.py so that it simply returns np.searchsorted(a, v, side='right'), emitting DeprecationWarning.
   (Remove this function in some future release.)
3. Rewrite the docstring of searchsorted in util/array.py accordingly.