SAPIResponder should handle header array well

[c9s]

The header array in the response array can be a List or a Map.

foreach ($headers as $h => $v) {
    if (is_numeric($h)) {  ... header in list }
    else if (is_string($h)) { ... header in map format }
}

[c9s]

Done in 86b6eba, 44561ec