Add examples

[LordMZTE]

Some examples would be great to figure out how to use this. These are some exmples which I think would be great, as they're not something usually done in neon:

• basic example of loading and running a JS file
• calling functions declared in JS files from rust
• loading a JS file as module (allowing import in the JS file)
• working with modules
  • importing modules
  • accessing module exports

The module examples would be particularly useful for me, as I wasn't able to figure those out yet.
I could contribute some examples (not all on the list however, as I've got no clue on how to work with modules)