Document the behaviour of Arithmetic/Counter operations max/min values

http://docs.couchbase.com/sdk-api/couchbase-c-client-2.4.0/group___l_c_b___a_r_i_t_h.html

The following should be documented in the API reference. In libcouchbase the values that are incremented and decremented are unsigned 64bit int values. So valid values are integers from 0 to 18,446,744,073,709,551,615 If you have the maximum value 18,446,744,073,709,551,615 and increment it by 100 it will wrap to 0 and keep incrementing, this will set the value to 99. If the value is 0 and you decrement the value by 1 it will stay at 0, it does not wrap.