* handle uint64 value in JSON
* Add integer_tests
* Add get_unsigned_integer() on ParsedJson::BasicIterator
* Write 'u' to tape when the value seems unsigned
* Add to handle 'u' element
* Brush up integer_tests.cpp
* Append tests/integer_tests in .gitignore
* Add comments to is_integer and is_unsigned_integer
* Get rid of dynamic allocation in ParsedJson::Iterator.
* Implement copy assignment operator for ParsedJson::Iterator.
* ParsedJson::Iterator is now a template class.