Add option to use Lua parser

[jasperhabicht]

Currently, the package only offers a pure TeX approach to parsing JSON. Lua has its own built-in Lua parser.

It would be great to add a way to make use of the Lua parser via the package using the existing commands as option.

[jasperhabicht]

Not straight-forward if all the existing functionality of the package (think of user-settable true or false strings or separators) should be provided.

The simplest way could be to use an existing lua parser (such as the one provided with lualibs.lua) and then loop recursively through the generated lua table adding the items to the property list.

However, this approach could still be optimized by re-writing the parser completely and directly add items to the property list without running over the lua table again.