Provide a default separator argument for join()
[ "set <<s>> [ turbine::string_join_impl <<A>> <<separator>> ]" ];
@pure
-(string s) join(string A[], string separator)
+(string s) join(string A[], string separator=",")
"turbine" "0.4.0" // "string_join"
[ "set <<s>> [ turbine::string_join_impl <<A>> <<separator>> ]" ];
