add more basic examples

[garyemerson]

This adds a few things that were non-obvious to me when starting out:

• Using simple arguments passed in from javascript (e.g. JsNumber)
• Using array arguments passed in from javascript
• Returning a JsArray from rust

I started writing the guide for these but I realize that was gonna take longer since I'm not the fastest writer. Definitely willing to write it but I could use some direction. For example, this perhaps belongs in "Handles and Memory" section (?) but also maybe not.