Refactor for Builder Pattern and Add custom HTML option

[stevenhuyn]

Todo

• Complete documentation

Closes #35
Makes Possible rust-windowing/winit#2816
Will Enable rust-windowing/winit#2852

Happy to change stuff, please feel free to suggest stuff.

fn main() {
    cargo_run_wasm::WasmRunnerBuilder::new()
        .css(
            r#"
        body { 
            margin: 0px; 
            display: flex;
            flex-direction: column;
            justify-content: center;
            align-items: center;
        }
        "#,
        )
        .html(include_str!("../../examples/web.html"))
        .build()
        .unwrap()
        .run();
}
``

[daxpedda]

Are two separate types really necessary? The build() function seems pretty useless:

WasmRunner::new().with_html(...).with_css(...).run();

... seems to do the trick.

EDIT: Just an idea, you should probably wait for @rukai's opinion on this.

[stevenhuyn]

Mr GPT suggested 2 structs but you make good points.

[rukai]

First a builder will be introduced as per #37 (comment)
Then I will come back to this PR and consider how we could introduce custom html into that builder.

[stevenhuyn]

legend, thanks man