A map like data structure based on Vec to represent a Graph with directed edges.

The goal is to be able to build a structure looking more like this:

     |
  \  |  /
 \ \ | / /
__\_\|/_/__
  / /|\ \
 / / | \ \
  /  |  \
     |

Instead of a tree like this:

  ____|____
__|__   __|__
|   |   |   |

Further goals:

• store and find node
• store edges
• [] graph traversal along the edges
• [] generator function to exhaustively discover all paths from one node to another
• [] possible weights on edges