Method writeUInt

Fleece/Support/JSONEncoder.hh:50–50

        void writeInt(int64_t i)                {_writeInt("%lld", i);}
        void writeUInt(uint64_t i)              {_writeInt("%llu", i);}
        void writeFloat(float f)                {_writeFloat(f);}
        void writeDouble(double d)              {_writeFloat(d);}