Support numpy size() and array.size

[ubaidsk]

fixes#1773

[ubaidsk]

This is ready.

[certik]

Thank you! This PR is good to merge.

Since we are doing it, in a new PR can you also please add a test like:

from numpy import size
a = empty((2, 3))
assert size(a) == 2*3
assert size(a, 0) == 2
assert size(a, 1) == 3

It will probably already work, but just in case. I usually use the size function like this, just like in Fortran.

[ubaidsk]

Since we are doing it, in a new PR can you also please add a test like:

Sure, thank you for the guidance. It seems the backends expect dimension value to start from 1, where as the axis attribute of numpy size() starts from 0. I fixed it by adding a constant 1 to the user provided dimension and added the test case in #1780.