Add Fenwick Tree

[czgdp1807]

Description of the problem

Fenwick trees are quite popular data structure and should be added to the package.

Example of the problem

References/Other comments

https://en.wikipedia.org/wiki/Fenwick_tree

[RashakDude]

@czgdp1807 Can you assign me this issue :)

[czgdp1807]

You can start working on this issue by proposing the API.
Please read the complete plan of action at https://github.com/codezonediitj/pydatastructs/wiki/Plan-of-Action-for-the-Projects
Thanks.

[aravind-karthikeyan]

Is this still open? Can I work on this issue?

[czgdp1807]

@aravind-karthikeyan Yes. Please see my above comment and start accordingly.