Allow download of large files on memory restricted machines, like a VPS

[miccoh1994]

Previously downloading even small files on machines with limited ram would result in a memory error. To overcome this the code has been adjusted to stream the file to disk in small chunks.

This has been tested on a VPS with 1gb RAM and works great. It may be worthwhile adding an optional arguement for chunk_size to the save function so that users may get a little more performance.