0.2.0

Added

• Added Env.read_env to read into the environment from a .env file.
• Added the optional env argument that defaults to acting as a noop.
• Made the default settings accessible directly from the class.
• Allowed None to be passed as a prefix.
• Added the inject_settings Meta option to inject inherited settings into the
  class namespace.

Changed

• Excluded nonupper attributes from default_settings.
• Restricted the settings module to the {module}:{class} formatting.
• Stopped normalizing lowercase prefixes.

Fixed

• Fixed Settings subclasses not inheriting the correct Meta sometimes.