surpport bool index

[zhaominxing208]

for example:
n [112]: arr = np.arange(12).reshape(3,4)

In [113]: i = np.array([True,False,True])

In [114]: i.nonzero()
Out[114]: (array([0, 2]),)

In [115]: arr[i]
Out[115]:
array([[ 0, 1, 2, 3],
[ 8, 9, 10, 11]])

In [116]: arr[i.nonzero()]
Out[116]:
array([[ 0, 1, 2, 3],
[ 8, 9, 10, 11]])