Move all built-in functions onto the new macro

[rscarson]

The builtins (src/functions/builtins/*) are all still using the older syntax, eg:

const LIST: FunctionDefinition = FunctionDefinition {
    name: "api_list",
    category: Some("network"),
    description: "List all registered APIs",
    arguments: Vec::new,
    handler: |_function, _token, state, _args| {
        let mut keys = state.apis.keys().collect::<Vec<&String>>();
        keys.sort();

        let definitions = keys
            .iter()
            .map(|k| format!("{}: {}", k, state.apis.get(*k).unwrap()));
        let t = definitions.collect::<Vec<String>>().join("\n");

        Ok(Value::String(t))
    },
};

Instead of the macro:

define_function!(
    name = sha256,
    category = "cryptography",
    description = "Returns the SHA256 hash of a given string",
    arguments = [function_arg!("plural", "input":Any)],
    handler = |function, token, state, args| {
        use sha2::{Digest, Sha256};
        let input = args.get("input").required().as_string();

        let mut hasher = Sha256::new();
        hasher.update(input);

        let s = format!("{:X}", hasher.finalize());
        Ok(Value::String(s))
    }
);

Examples have been moved over but these still need to be redone in the new syntax