Top level `Graph` API

I think consistency over the data viz libs in the stack can have huge benefits. Therefore, I suggest to either re-write this lib to follow the same patterns, or gradually introduce a top-level API.

For example, in Plotly.NET we have something like this:

```fsharp
Chart.Point(x=[...], y = [...])
```

Internally, there are multiple things happening, as in plotly.js there is no trace named "point". `Chart.Point` is a simple top-level API that removes the need for deep plotly.js knowledge.

in Cyjs.NET (or Cytoscape,NET, see #11 ), we could have something like this:

```fsharp
Graph.Tree(...) // creates a graph that uses taxi edges per default
Graph.Circle(...) // creates a graph using circular layout per default
```

not sure about the types of graphs that make the most sense besides `Graph.Tree` though, so i'd love some input