Add `getMap` and `getList` back to Std.Table (safely)

[jparoz]

With the trivial implementation, there's nothing to stop a user producing incorrectly typed values in Huck like so:

goodList = Std.List.collect [123];
goodMap = Std.Map.collect [(2, "two")];
badMap = getMap $ mkTable goodList goodMap;

This produces a Lua table like

badMap = {123, "two"}

which is interpreted in Huck as

badMap : Std.Map.Map Int String;

but the element at key 1 has the wrong type of value!

Need a solution in order to put these functions back in.