1. First, allocate space for m `struct pixel *` values, where m is the height of the image.  Each pointer will eventually point to one row of pixel data.
2. For each pointer you just allocated, initialize it to point to heap-allocated space for an entire row of pixel data.
3. Use the given file and pixel_array_offset to initialize the actual struct pixel values. Assume that `sizeof(struct pixel) == 3`, which is consistent with the bitmap file format. NOTE: We've tested this assumption on the Teaching Lab machines, but if you're trying to work on your own computer, we strongly recommend checking this assumption!
4. Return the address of the first `struct pixel *` you initialized.