gemfile: use HTTPS connection to download gems
gitignore: add module.tar.gz to gitignore
tests: add Docker images and Makefile to be able to run tests locally
gitignore: ignore pkg/ directory
Makefile: run check on make all
README: document the testing workflow
README: add the new sections to the Table of contents
tests: add centos6 and centos7 to the tested platforms
README: update supported platforms
Merge pull request #20 from ihrwein/f/fig

F/fig