Investigate moving away from requiring #[wasm_bindgen(start)] attr

[thedodd]

Per some discussion here https://discordapp.com/channels/701068342760570933/701068343431528490/748623604563837030 it looks like we may be able to move away from requiring folks to use the #[wasm_bindgen(start)] attribute.

Also see rustwasm/wasm-bindgen#1057 (comment)

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todo

• update the readme example to use fn main without the #[wasm_bindgen(start)] attribute.

[siku2]

Finally got a chance to try this out and I'm happy to report that this already works out of the box. You can see it being used here.

So this is just a matter of updating the template / documentation.

[thedodd]

Awesome! Thanks for pointing this out @siku2. I'll add a TODO item to this issue for removing said attribute from the main function. Overall this should help to reduce cognitive load a good bit.