This commit fixes the following issues:

- Partially addresses #7 by proposing a way to check README file syntax
  through python packaging (twine)
- It introduces arguments to the subcommands `ci pypi` and `ci readme`
  that provide the package path instead of letting it figure out from
  the environment/variables (also addresses #8 in this case)

- Addresses issue #8 by making it explicit the use of environment
  variables. Don't look-up env variables outside the option parsing
  context.
- Try a mitigation for issue #2 (garbled output)
- Implement more formalized command-line options based on argparse
  (cannot use click at this stage)