Requesting to have Nlohmann.JSON added as a possible external dependency alongside Boost

Hi, everyone.

This is related to the that other issue I opened about Nlohmann.JSON and RapidJSON.  Please look into that as well.  I hope a solution for that will be found at some point.

Anyway, I'd like for there to be an option to use other dependencies as external as well as aside from just Boost, just in case people have them on their computers.  Like how I have Nlohmann.JSON.  