Add Bron Kerbosch algorithm to find maximal cliques

[TripleCamellya]

A clique in an undirected graph is a subset of vertices where every two distinct vertices are adjacent. In other words, a clique is a complete subgraph where each vertex is connected to every other vertex within the subset.

A maximal clique is a clique that cannot be extended by including one more adjacent vertex. That is, a maximal clique is a clique that is not a subset of any other clique in the graph. It is the largest clique that can be formed starting from a given vertex or a given subset of vertices.

Bron–Kerbosch algorithm is an enumeration algorithm for finding all maximal cliques. It is widely used in application areas of graph algorithms such as computational chemistry.

Here is wiki:

https://en.wikipedia.org/wiki/Bron%E2%80%93Kerbosch_algorithm

Task:

1. Implement a new API for maximal cliques problem.
2. Add Bron-Kerbosch algorithm for maximal cliques problem.
3. Add related doc for find_maximal_cliques.
4. Add related tests.

[TripleCamellya]

I have already completed the tasks mentioned above. I will submit a new PR after receiving a reply to my previous one.

Example:

>>> from pydatastructs import Graph, AdjacencyListGraphNode
>>> from pydatastructs import find_maximal_cliques
>>> V1 = AdjacencyListGraphNode('V1')
>>> V2 = AdjacencyListGraphNode('V2')
>>> V3 = AdjacencyListGraphNode('V3')
>>> V4 = AdjacencyListGraphNode('V4')
>>> G = Graph(V1, V2, V3, V4)
>>> G.add_edge('V1', 'V2')
>>> G.add_edge('V2', 'V1')
>>> G.add_edge('V2', 'V3')
>>> G.add_edge('V3', 'V2')
>>> G.add_edge('V1', 'V3')
>>> G.add_edge('V3', 'V1')
>>> G.add_edge('V1', 'V4')
>>> G.add_edge('V4', 'V1')
>>> find_maximal_cliques(G, 'bron_kerbosc')
[{'V1', 'V3', 'V2'}, {'V1', 'V4'}]