A directed graph library for PureScript.

The directed graph pictured above can be represented with an `AdjacencyList`

.
An adjacency list is a list of tuples that contain a vertex and a list of edges
to its adjacent vertices. A `Graph`

can be constructed from an `AdjacencyList`

.

```
let edges = fromFoldable $
[ Tuple 'A' (fromFoldable [Tuple 'B' 1, Tuple 'C' 2])
, Tuple 'B' (fromFoldable [Tuple 'A' 1, Tuple 'D' 3])
, Tuple 'C' (fromFoldable [Tuple 'A' 2, Tuple 'D' 4])
, Tuple 'D' (fromFoldable [Tuple 'B' 3, Tuple 'C' 4])
, Tuple 'E' (fromFoldable [Tuple 'F' 1])
, Tuple 'F' (fromFoldable [Tuple 'E' 1])
, Tuple 'G' (fromFoldable [])
]
let graph = fromAdjacencyList edges
```

The `size`

function returns the number of vertices in a graph.

```
size graph
-- 7
```

The `vertices`

function returns a list of the vertices in a graph.

```
vertices graph
-- ['A', 'B', 'C', 'D', 'E', 'F', 'G']
```

The `isAdjacent`

function returns true if two vertices are connected by an edge.

```
isAdjacent 'A' 'B' graph
-- true
```

The `weight`

function returns the weight of the edge between two vertices.

```
weight 'A' 'B' graph
-- Just 1
```

The `adjacent`

function returns all vertices connected to a vertex by an edge.
The `adjacent'`

function will also include the weight of the edges.

```
adjacent 'A' graph
-- ['B', 'C']
adjacent' 'A' graph
-- [Tuple 'B' 1, Tuple 'C' 2]
```

The `shortestPath`

function calculates the shortest path between two vertices
using Dijkstra'a
algorithm.

```
shortestPath 'A' 'D' graph
-- ['A', 'B', 'D']
```

The `connectedComponents`

function calculates a list of connected components in a graph.

A connected component is a maximal subgraph in which any two vertices are connected to each other by a path.

```
connectedComponents graph
-- [Graph, Graph, Graph]
```

An empty graph can be constructed and updated.

```
(insertEdge 'A' 'B' 1 <<< insertVertex 'A' <<< insertVertex 'B') empty
-- Graph
```