Allow user to use the function named main for #[ewasm_main]

[yanganto]

#[ewasm_main] is a macro to wrap a function to with main function for ewasm.
Currently, the function wrappered is not allow to be name as main.

For a better UX, it is good to rename the function when its name is main, and not panic.

Please help with this issue.

Relate PR #35
https://github.com/second-state/SewUp/pull/35/files#diff-6f891a9986798db9fa65d7dd779c98c44afa864739fdd39a556eafdcdb75a943R19
https://github.com/second-state/SewUp/blob/main/sewup-derive/src/lib.rs#L19

[yanganto]

This is not a issue with nesting functions