Write a function in python, index(arr, value) to find indices of elements equal to some value in a Numpy array. The input arr is a 1-d numpy array, and input value is the value to search for. The function should return the index of the value. If the value occurs for multiple times, then all the indices should be returned as a 1-d numpy array. For example, if arr=[1 0 2 0 3 0 4 0 5 0 6 7 8 0], then index(arr,3) should return 4, and index(arr,0) should return [1 3 5 7 9 13].