Add distributed storage backend using raft

[ragul28]

Raft consensus protocol helps to build distributed application cluster. This makes app to run as daemon on server side.

Available major libraries are,

• hashicorp-raft
• etcd

This feature & #5 need to be work in conjunction to achieve distributed storage layer.

[ragul28]

Planning to go head with hashicorp-raft for the simplicity compared to etcd version. During the implementation other factors may favor etcd-raft.