Process all input from stdin.

@params opts {Object} Bunyan options object.
@param stylize {Function} Output stylize function to use.
@param callback {Function} `function ()`
function processStdin(opts, stylize, callback) {
    var leftover = '';  // Left-over partial line from last chunk.
    var stdin = process.stdin;
    stdin.resume();
    stdin.setEncoding('utf8');
    stdin.on('data', function (chunk) {
        var lines = chunk.split(/\r\n|\n/);
        var length = lines.length;
        if (length === 1) {
            leftover += lines[0];
            return;
        }

        if (length > 1) {
            handleLogLine(null, leftover + lines[0], opts, stylize);
        }
        leftover = lines.pop();
        length -= 1;
        for (var i = 1; i < length; i++) {
            handleLogLine(null, lines[i], opts, stylize);
        }
    });
    stdin.on('end', function () {
        if (leftover) {
            handleLogLine(null, leftover, opts, stylize);
            leftover = '';
        }
        callback();
    });
}