Module pl.import_into
PL loader, for loading all PL libraries, only on demand.
 Whenever a module is implicitly accesssed, 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