Add 'Loader' example

[dcodeIO]

As promised on the Discord, I've made an example covering the very basics of utilizing the loader.

• Example 1: Passing a string from WebAssembly to JavaScript.
• Example 2: Passing a string from JavaScript to WebAssembly.
• Example 3: Calling JavaScript imports with WebAssembly strings.
• Example 4: Passing an array from WebAssembly to JavaScript.
• Example 5: Passing an array from JavaScript to WebAssembly.
• Example 6: WebAssembly arrays of WebAssembly strings.
• Example 7: Using custom classes.

This should give everyone interested a quick start with recipes to perform the most common tasks. As usual, my perspective might be a little trees in the woods here, so let me know where I am assuming something that isn't trivial :)

[MaxGraey]

I guess will be great also add 7th example which demonstrate how do something like this:

class Complex {
   re: f64
   im: f64
};

export function getComplexMatrix(): Complex[][] {
  ...
}

[dcodeIO]

Initially considered making another example like "Loader Advanced", but I think you are right and I should just add it here, as there aren't a lot of advanced custom classes scenarios anyway.

[MaxGraey]

Do you think move it to AssemblyScript/examples repo?

[dcodeIO]

Yeah, figured that a separate repo makes sense with increasing example count. Loader example is here: https://github.com/AssemblyScript/examples/tree/master/loader