Pushes and retrieves aeson Values to and from the Lua stack.

• JSON null values are encoded as light userdata containing the NULL pointer.
• Objects are converted to string-indexed tables.
• Arrays are converted to sequence tables and are given a metatable. This makes it possible to distinguish between empty arrays and empty objects. The metatable is stored in the registry under key 'HsLua JSON array'' (see also jsonarray).
• JSON numbers are converted to Lua numbers, i.e., Number; the exact C type may vary, depending on compile-time Lua configuration.