Standard commit format

[tisonkun]

Currently commits of TubeMQ don't have a standard format. A standard format helps search/filter commits in log, understand the purpose of a commit or a pull request and so on.

Here are several alternatives coming from other project.

1). Study from Spark & Flink, [TUBEMQ-<issue-number>][<component>] .... Concerns here would be what issue tracker we use(for now it seems we just use GitHub issues) and what components we split into.
2) Study from AngularJS. It is well-known and due to the content is too long to inline I just link to the guidelines page.
3) Study from Pravega, Issue <issue-no>: .... Details are here.

Any insight would be helpful :-)