Le badge

[skip-ci]
Adds terminal-notifier-guard

[ci-skip]
Moves dev and test gem dependencies to Gemfile

- adds yard for documentation
- removes dead code
- updates .gitignore
Extract configuration into Configurable

- watched with Guard
- both Putio and Putio::Client are configurable
- configuring Putio will pass the config to the underlaying client
- use safe defaults for every options except access_token
Cleanup Connection
Adds Resource::File and list_files
Adds an integration test, updates usage in README