Advanced JSON handling with arrays

[David Bovill]

I've been using mergJson for a number of years, and construct json using
arrays then convert them to json for rpc. I've been porting this to
web/wasm export and hit the block that mergJson is not available for web.

I've tried the built in library but it does not work the same for nested
arrays and I can only get it working for simple structures.

Any advise on how to handle JSON properly?