Cloning sometimes crashes with big files

[mjp0]

Sometimes when you try to download a bigger file, datagram unexpectedly closes the connection. I suspect this might be due to a sudden memory spike with serialization and encryption.

[mjp0]

Turns out this is caused by a protocol level limitation for message sizes (8MB). This is not a big deal because I've already been designing an alternative, more efficient way of storing bigger data for #44 and #41. When both of those are combined, message sizes will never reach the 8MB limit.

No changes in public API required so still in the right track for v1.0.