Support multi-byte characters (Unicode)

[bluedasher13]

RAW JSON Data (errorData.json):

{"DAMAGE":"圓圓圓圓圓圓圓"

Test Code:

$parser = new \Seld\JsonLint\JsonParser();
$exception = $parser->lint(file_get_contents('errorData.json'));
echo $exception->getMessage();

【Before fix】：

Result:

Parse error on line 1:
...�圓圓圓圓圓圓"
----------------------^
Expected one of: '}', ','

Contains incorrect characters, and fails to json_encode($message):

var_export(json_encode($exception->getMessage()) === false);
var_export(json_last_error_msg() === 'Malformed UTF-8 characters, possibly incorrectly encoded');

【After fix】：

Result (after fix):

Parse error on line 1:
{"DAMAGE":"圓圓圓圓圓圓圓"
------------------^
Expected one of: '}', ','

Not contains incorrect characters, and succeed in json_encode($message):

var_export(json_encode($exception->getMessage()) === '"Parse error on line 1:\\n{\\"DAMAGE\\":\\"\\u5713\\u5713\\u5713\\u5713\\u5713\\u5713\\u5713\\"\\n------------------^\\nExpected one of: \'}\', \',\'"');
var_export(json_last_error_msg() === 'No error');

[Seldaek]

Thanks but this changes way too much code for what is needed IMO.

I think it should be enough to fix this in getPastInput, getUpcomingInput and getFullUpcomingInput as those are used to generate exceptions. The rest works fine as is and does not need changing.

And for those 3 functions, it is ok to use mb_* functions if they are present, but we need to check with function_exists first, otherwise call the regular str* functions. mbstring cannot be a requirement of this package.