Add get_version_info endpoint

[psheth9]

Fixes #10

This PR does following things:

• Call /info endpoint with backoff exp retry to fetch captive core version
• Reuse getBucketListSizeAndProtocolVersion to fetch protocol version
• Update MakeFile to populate version, commit_hash and build_time_stamp

get_version_info Response -->

        Version            string `json:"version"`
	CommitHash         string `json:"commit_hash"`
	BuildTimestamp     string `json:"build_time_stamp"`
	CaptiveCoreVersion string `json:"captive_core_version"`
	ProtocolVersion    uint32 `json:"protocol_version"`

[Shaptic]

I know it's still a draft but I was just drivin' by