lab3: Add minor clarifications in function descriptions

Add short lines clarifying how Warshall and Floyd differ (as that tends to be a common question).

Also clarify that set_tail() is just an alias for cons() (and reflect this in the actual implementation) to avoid any confusion for why there's two methods which do the same thing.

Finally, rework the example for Dijkstra's algorithm to make it slightly more interesting (actually have to get to c via b, instead of just going to all nodes from a). This essentially undoes the "Fix dijkstra info text" commit by changing the example setup to correspond to the original result (as I belive it was inteded), instead of changing the result to match the original (trivial) example setup.

Signed-off-by: Simon Sundberg simon.sundberg@kau.se