Update the `inv --test.local` command to ensure that tests are run against
the correct version of the package. The invoke command has been updated to:
- Ensure the `anybadge` command is not available on the system to start with
- Ensure `pip` is available
- Pip install the local project
- Run tests
- Pip uninstall `anybadge`
The net result is that invoke will be more robust in terms of making sure the
installed version is in sync when running CLI tests.
* Make `build_examples.py` callable from python
* Allow tests to run from outside project directory
* Add invoke tasks
* Add server tests
* Run travis tests against wheel package instead of local code
* Update `badge.write_badge()` to support `pathlib.Path`
* Update `CONTRIBUTING.md`
