Add real tests, add coverage information

[bittner]

Missing Tests

As of version 0.1.0 the "tests" executed by tox:

• don't fail when one or more of the sections of the test YAML file are not recognized
• don't test whether a missing codeship.yml file results in the expected error message
• don't test whether an invalid YAML file is handled gracefully (in fact, yaml.parser.ParserError is not being caught yet)
• don't test whether both single-line sections (e.g. section_name: command_name) and multi-line sections execute correctly
• don't ensure that empty sections are handled gracefully (TypeError: 'NoneType' object is not iterable)
• don't test whether the system command calls actually execute certain shell commands
• don't test whether a failing command aborts the execution chain immediately, yielding a non-zero exit code

Expected Implementation

1. Those tests should be implemented (in py.test) and be run with coverage.
2. The coverage information (coveralls) should show as a badge on top of the README.