Feature: loading from a file and dumping to a file.

[mratsim]

It doesn't seem like jsony supports loading from a file, which a user needs space to hold 2x the json size in memory.

[treeform]

I don't like the nim's file streaming APIs as it slows everything down by 10%. I can see supporting some thing like mmap. In fact probably most file reads should be mmaps. Also having json files this large is probably not a good design. And I deal with terabytes of json files...