feat: Use the Handles, Luke!

[shanecelis]

I was only planning to file issue #426 tonight, which states the problems I was having. I thought if I poked around I'd find the implementation reason for why what I suggest there wouldn't work. So I made a branch and rolled up my sleeves, and I was able to pretty quickly get exactly what I wanted.

Handles

In the issue I suggest doing away with ScriptId. As I worked with the implementation, it became clear I actually wanted to redefine it.

// OLD
// type ScriptId = Cow<'static, str>; 
// NEw
type ScriptId = AssetId<ScriptAsset>;

Beyond that I made it so ScriptComponent holds Handle<ScriptAsset>s. The nice thing about this is you can use this pattern:

ScriptComponent(vec![asset_server.load("foo.lua")])

No need to store a strong handle somewhere so your script isn't unloaded. However, if you rely on that behavior you can still do that like you do with any other asset-based item using weak handles.

let strong_handle = asset_server.load("foo.lua");
ScriptComponent(vec![strong_handle.clone_weak()])

This preserves the semantics of the current release.

ScriptAsset loading versus evaluation

In this PR the static scripts are handled essentially the same as before except they can retain handles (both strong and weak).

The non-static scripts are not evaluated until they are added to a ScriptComponent. Then they are evaluated in order, sequentially.

ScriptAsset change

I suggested a change to ScriptAsset and that survived this refactoring.

pub struct ScriptAsset {
    /// The body of the script
    pub content: Box<[u8]>,
    /// The language of the script
    pub language: Language,
}

I also provided a ScriptSettings where one can provide a definite language. None will use the file's extension.

asset_server.load_with_settings("hello.p8", |settings: &mut ScriptSettings| {
   settings.language = Some(Language::Lua);
});

One downside about ScriptSettings is it required adding "serde" with the "deriv" feature as a dependency.

Example

I updated the Game of Life to work with Lua and Rhai and all its console options.

Remaining work

I have not tried to exercise any other languages or even do much with the tests. But I'd be happy to move this forward to handle the rest with some consensus that that's the right direction.

[shanecelis]

I got the tests compiling and running. There are 9 failures with features 'lua' and 'rhai'.