getting started integration tests

[mwspracklen]

Working on adding integration tests per #777 . I've created a quick example of how I'm planning to implement this in examples/sqlite/getting_started_step_2 . Initial thought is to add a tests directory with a test that uses assert_cmd to run the relevant binaries for each step. Considering writing in some calls to diesel to examine the database as well, let me know if that's the correct route or if just verifying binary output is sufficient.

In examples/sqlite/getting_started_step_2 I ran the following to test
echo "DATABASE_URL=file:/tmp/test.db" > .env; rm -f /tmp/test.db ; diesel migration run; cargo test; rm -f .env

[VicVerevita]

Hello, I have made the postgresql and mysql tests for getting started in #4087. Tell me if you will finish the sqlite tests or if I should add them as well in my PR.

[mwspracklen]

I was planning to wait for feedback, but it's probably better if there's one PR for the whole issue, so you can take the whole thing and I'll delete this PR

[weiznich]

It would have been better to at least pull in the commit that @mwspracklen has done, but now it is at it is.