Module pl.import_into
PL loader, for loading all PL libraries, only on demand.
Whenever a module is implicitly accessed, the table will have the module automatically injected.
(e.g. _ENV.tablex)
then that module is dynamically loaded. The submodules are all brought into
the table that is provided as the argument, or returned in a new table.
If a table is provided, that table's metatable is clobbered, but the values are not.
This module returns a single function, which is passed the environment.
If this is true, then return a 'shadow table' as the module
See the Guide