Construct a new jss::actor instance running the specified
            function.
          
template<typename Func,typename ... Args> explicit actor(Func&& f,Args&& ... args);
                  Constructs a jss::actor
                  instance running a copy of the specified function on a new thread,
                  with copies of the specified args. The copies are contructed as-if
                  Func temp(std::forward<Func>(f)) and ArgsN
                  tempN(std::forward<ArgsN>(argsN)) for each element in Args....
                
                  std::system_error if the actor thread
                  cannot be started; any exceptions thrown by the copy or move constructor
                  of Func.
                
                  this->valid()
                  returns true.
                
            #include <jss/actor.hpp>