feat: enumerate overloaded functions if they are nameless

[mattsse]

Motivation

Close #543

Solution

generate aliases using the call's indices if the function params are nameless like

    abigen!(
        ConsoleLog,
        r#"[
            log()
            log(string, string)
            log(string)
    ]"#
    );

becomes

enum    ConsoleLogCalls {
    Log0,
    Log1(...),
    Log2(...),
}

PR Checklist

• Added Tests
• Added Documentation
• Updated the changelog

[gakonst]

LGTM