Panic when parsing message about nmea-parser

[matt24smith]

This is a challenging issue, as far as I can tell, the code in this package is correct and the issue arises with malformed messages and dependent libraries.

The panics appear to be caused by malformed UTC date response and binary application messages - I only care about vessel data, so in my case, I can safely discard these before decoding using the following function.

/// discard UTC date response and binary application payloads before decoding them
pub fn msgfilter(msg: &str) -> Option<&str> {
    if &msg.chars().count() >= &15 && &msg[..12] == "!AIVDM,1,1,," {
        match &msg[12..13] {
            "0" | "1" | "2" | "3" | "A" | "B" => match &msg[14..15] {
                ";" | "I" | "J" => None,
                _ => Some(msg),
            },
            _ => Some(msg),
        }
    } else {
        Some(msg)
    }
}

I imagine not everybody will need the binary application messages, would it make sense to skip these by default with an option to decode?