New warnings

[vitaut]

    25>C:\projects\cppformat\format.h(781): warning C4244: 'argument' : conversion from 'const double' to 'fmt::ULongLong', possible loss of data [C:\projects\cppformat\test\printf-test.vcxproj]
                 C:\projects\cppformat\format.h(2662) : see reference to class template instantiation 'fmt::internal::IsConvertibleToInt<double>' being compiled
                 C:\projects\cppformat\test\printf-test.cc(134) : see reference to function template instantiation 'std::string fmt::sprintf<double>(fmt::StringRef,const double &)' being compiled

[vitaut]

Fixed in 275d1ab.

[vitaut]

Need to find another way to fix warnings because of #139.

[vitaut]

Fixed in 0e8fcd4.