Edited Issue: Comparision error [212]

Hi there,
I tried to compile casablanca again and stumbled over this error (only with gcc-4.9)
`
casablanca/Release/src/json/json_parsing.cpp:359:19 error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
if (value >((int) (ULLONG_MAX / 10)) || (value == ((int)ULLONG_MAX/10) && next_digit >((int) ULLONG_MAX%10)))
`
I think that such error do not have to exsist.

Cheers,
Henry