Add TravisCi integrations

[DrEdi]

• [x] Configure Travis CI to run pre-commit utility under python 3.5: (.travis.yml)

  language: python
  python: 3.5
  cache: pip
  before_install: pip install -U pre-commit
  script: pre-commit run --all-files

• [x] Add badge stating master in its URL, not current branch

[webknjaz]

Please re-check common commit practices. Also, please read info about doing squash via git rebase --interactive, so that you could rewrite your feature branches and make their history easy-to-read and well-understandable.