Next to last release before workshop

This is the release we'll be using for the workshop unless major bugs emerge before then.

v0.2.0

February 2, 2019 release:

• Refactored the Docker system2 interface. The book still compiles; everything the book references has the same API it did before, although I think it's better documented now.
• The vignette is now built with the self-contained = FALSE option. This keeps the vignette rendering from crashing in pandoc on Windows. See issue #35
• Added functions to do docker ps and docker images and return the results as tibbles.
• Added a function to build the DVD rental image. I also added a test that runs it from start to finish.
• Added a script to install on Fedora Linux.
• Added RSQLite as a dependency so the DBI example in the book will run.