Normalize ordinal dates

[gRegorLove]

Fixes #167

[Zegnat]

I would advise against using exceptions when what you really want is just a logic branch.

Why not something like this?

function normalizeOrdinalDate($dtValue) {
    list($year, $day) = explode('-', $dtValue, 2);
    $day = intval($day);
    if ($day < 367 && $day > 0) {
        $date = \DateTime::createFromFormat('Y-z', $dtValue);
        $date->modify('-1 day'); # 'z' format is zero-based so need to adjust
        if ($date->format('Y') === $year) {
            return $date->format('Y-m-d');
        }
    }
    return '';
}

[gRegorLove]

Good point, @Zegnat. I think I started with Exception because I was going to check DateTime::getLastErrors() for warnings about invalid dates but ended up going a different route.

Don't code tired. :)

[Zegnat]

Now that the exception throwing is gone, I think it all looks good!

[aaronpk]

This function isn't properly validating the input, but I see that it is only ever called after the input is guaranteed to be in the format \d{4}-\d{2}. Can you add a comment to the function definition that explains that this function can only be called with pre-validated input?

[aaronpk]

see inline comment