Detect and mask secrets

This MR provides logic to detect and mask the following secrets:

• basic authentication
• jwt
• twilio tokens
• artifactory credentials
• sendgrid tokens
• azure storage keys
• discord tokens
• secret-sounding variable names. Use cases we're able to detect now - https://github.com/Yelp/detect-secrets/blob/master/tests/plugins/keyword_test.py#L126

Ref #12 (closed)