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