Add 'setup' and 'teardown' method.

[marcofavorito]

Proposed changes

Add a setup() and teardown() method to the Agent class.

Fixes

Fixes #332

Types of changes

What types of changes does your code introduce to agents-tac? Put an x in the boxes that apply

• [ ] Bugfix (non-breaking change which fixes an issue)
• [X] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Put an x in the boxes that apply.

• [X] I have read the CONTRIBUTING doc
• [X] I am making a pull request against the develop branch (left side). Also you should start your branch off our develop.
• [X] Lint and unit tests pass locally with my changes
• [ ] I have added tests that prove my fix is effective or that my feature works
• [X] I have added necessary documentation (if appropriate)
• [X] Any dependent changes have been merged and published in downstream modules

Further comments

The setup() method is called in the _run_main_loop() function, before the while loop. The teardown() method, on the other hand, is called after the same while loop, just before the call to the stop() method.