only 1d indexing currentlysupported with axis arg

[joshua-gould]

Unable to run the example "Use the axis arg in order to do a sum-aggregation on three rows simultaneously" in README.md

import numpy as np

import numpy_groupies as npg

a = np.array([[99, 2, 11, 14, 20],
              [33, 76, 12, 100, 71],
              [67, 10, -8, 1, 9]])
group_idx = np.array([[3, 3, 7, 0, 0]])
x = npg.aggregate(group_idx, a, axis=1)

Error:

Traceback (most recent call last):
  File "test.py", line 9, in <module>
    x = npg.aggregate(group_idx, a, axis=1)
  File "numpy-groupies/numpy_groupies/aggregate_numba.py", line 563, in aggregate
    return func(group_idx, a, size, fill_value, order, dtype, axis, **kwargs)
  File "numpy-groupies/numpy_groupies/aggregate_numba.py", line 51, in __call__
    iv = input_validation(
  File "numpy-groupies/numpy_groupies/utils_numpy.py", line 317, in input_validation
    raise NotImplementedError(
NotImplementedError: only 1d indexing currentlysupported with axis arg.