Function has_path 

pub fn has_path<V>(
    q: &GraphQuery<V>,
    weight: &TraversalWeight<V>,
    from: &Pattern<V>,
    to: &Pattern<V>,
) -> bool
where
    V: GraphValue + Clone,
    V::Id: Clone + Eq + Hash + Ord,

Returns true if a path exists from from to to.

Delegates to shortest_path.