Otlet

- implement PackageObject.releases
- add util.py

- remove `requests` dependency in favor of stdlib's `http.client` implementation
- bump required python version down to 3.7
- no 3.6 due to dataclasses import in `types.py`

- add --version argument, used to print current otlet version
- add `exceptions.py` and implement "custom" exceptions
- add differentiation between when no package found in API and when package version not found

- version bump for PyPI push

- initial release