ENH: to/from_scanner() should accept arrays of coords

[bennyrowland]

Currently the to_scanner() and from_scanner() functions take three arguments: x, y, z and return an numpy array. It would be convenient if the functions could handle a numpy array as an input for consistency, this would also allow passing in an array of coords to be transformed all at once, for example from meshgrid(). On the other hand, in the case where the user wants to pass in simple known x, y and z values, this requires them to be wrapped in a tuple, being called like to_scanner((x, y, z)), similarly to the numpy.ones() function. This could be addressed by permitting either 1 or 3 *args and interpreting either as an ndarray of shape [...3] or 3 floats.