Implement externalized WASM build

[mochaaP]

An alternative to #97.
See #96 for more info.

[guybedford]

I'm still curious how the fs.readFile is supposed to work at runtime in a distribution? Shouldn't all of this be happening at a binary level somehow?

[khardix]

@mochaaP I tried to grok the code and perhaps come with an explanation myself, but to no avail. Adding some docs (README? Comment block in code?) would probably help any future maintainer to understand what we are trying to archive here and why it's done in this specific way.

@guybedford Aside – thanks for the patience with this change, I really appreciate it!

[mochaaP]

Added comments to explain the load process. If something is still unclear, please point it out :)

[guybedford]

@mochaaP thanks for adding comments, my question though specifically is how you are hooking the readFile call in the Node implementation to support inlining the binary in the runtime?