Add readdir builtin and bump install to 0.2.1

Squashed commit of the following:

commit bdff436162943f7665b645c4716e29a994855806
Author: mtso <~@mtso.io>
Date:   Sat Aug 14 17:24:33 2021 -0700

    Change module resolution

commit 95f2189c649ffe170f8eb5f59ea2586ab1325aeb
Author: mtso <~@mtso.io>
Date:   Fri Aug 13 10:28:38 2021 -0700

    Improve builtins

commit ed8cdacc56b9490eebfb600398313a0de4b0f568
Author: mtso <~@mtso.io>
Date:   Thu Aug 12 21:26:25 2021 -0700

    Update tail-call opt and improve builtins for wasm loading

Fix ci

Fix module load scoping

Add module loading as runtime fn

Add returns