Add support for roblox-ts

[vocksel]

Problem

Currently there is no support for roblox-ts (reported in #12 and flipbook-labs/flipbook#198) due to us not creating a unified _G table for modules to use and from the runtime library being cleared from the cache

Solution

1. Added support for tracking assignments to _G
2. Added a special case to skip the roblox-ts runtime when clearing a module's consumers from the cache
3. Added the clearModule method which is can be called to clear a single module (and its consumers) from the cache
4. clearModule is called automatically on cached modules that undergo an ancestry change or a change to the Source property

Fixes #12, fixes #13