Detect rate-limiting and add code to log and wait.
lib/credentials -> lib/cli/credentials
Attempt login using the API key in solvebio shell. Login() now looks for and accepts an API key. SoveBio credentials file is no longer shared with .netrc.
Merge/rename old credentials test.
Merge branch 'dev' into feature/netrc
Merge pull request #13 from solvebio/feature/netrc

Rework API-key/login interaction. Add request rate-limiting.