Add a test project for integration tests
Add first version of Releaser

This is the code that interacts with git and builds an artifact.
Add integration tests that create an artifact and runs it
Use the right branch for the specified environment

E.g. build from master for production and staging for staging.
Rewrite the command execution in the integration tests

Much easier to debug now with EXEC_DEBUG=y, which will print each command as it's run, and it's output.
Add integration tests for the SHAs in artifact names
Move jara into the development group in the test project's dependencies
Add Puck as a dependency

Should have been added long ago, but I had put it in Gemfile
Run the unit tests in a temporary directory

Mostly to control the name Jara picks for the artifact
Add Releaser#release for uploading to S3
Don't build an artifact if one already exists
Change how the S3 client is created

Aws.s3 checks for credentials, so wait to call it until absolutely necessary.
Don't build or upload when there already exists a release