Broken API: can't use Payload{{my_string_key, my_string_value}}
Broken API: can't use Payload{{my_string_key, my_string_value}}

The Pair constructor accepts only r-value references which forces to use string variables as:
Payload{{my_string_key.c_str(), my_string_value.c_str()}}.
Added const reference to strings constructor
whoshuu/cpr,whoshuu/cpr,whoshuu/cpr