graph: add is_connected (#163)
* graph: add is_connected * simplify truth comparisons Co-authored-by: Andreas Klöckner <inform@tiker.net> * remove validation Co-authored-by: Andreas Klöckner <inform@tiker.net>
* graph: add is_connected * simplify truth comparisons Co-authored-by: Andreas Klöckner <inform@tiker.net> * remove validation Co-authored-by: Andreas Klöckner <inform@tiker.net>