cpp/experimental/ostream joiner/ostream joiner

1) Constructs the iterator with the private member initialized with, the private delimiter member initialized with , and the private "first element" flag set to.

2) Constructs the iterator with the private member initialized with, the private delimiter member initialized with , and the private "first element" flag set to.

3-4) Implicitly declared copy/move constructor that copy/move constructs the private stream pointer, delimiter, and "first element" flag members.