Added convenience functions to serialize JSON to QStrings.
Added a check if parsing a number to int/uint (smaller than qlonglong/qulonglong) is possible.

Signed-off-by: Alexandr Zarubkin <me21@yandex.ru>
Merge pull request #25 from me21/master

Added convenience functions to serialize to QStrings. Added a check to parse numbers to int/uint (smaller than qlonglong/qulonglong)