ENH: Allow meshgrid to take 1D and 0D inputs

I work with many problems that are generic in their dimensionality (1D, 2D, 3D, etc).  Patterns like the following example occur frequently, where, e.g., there is a number of nodes for each dimension, yet the code is agnostic to the number of dimensions.

    nodes = [5, 6, 7]
    indices = [np.arange(n) for n in nodes]
    dims = np.meshgrid(*indices)

Currently, `numpy.meshgrid` does not allow cases like

    nodes = [5]

and thus, I am required to handle a special case for 1D every time I want to use `meshgrid`.

This patch allows `meshgrid` to take a single argument, which allows such generic patterns to be useful.