v0.3.9

Added

• Added top-level documentation with examples for each auth flow and general usage.
• Added constructors for the auth flow structs.
• Renamed AuthCodeGrantFlow, AuthCodePKCEGrantFlow and ClientCredsGrantFlow to AuthCodeFlow, AuthCodePkceFlow and ClientCredsFlow respectively.
• Added the AuthCodeClient, AuthCodePkceClient and ClientCredsClient type aliases for each of the client's authflows.
  These are what you should use when referring to the Client type.

Changed

• Client::authenticate() doesn't take scopes anymore for the client credentials flow, as they were needless.
• Moved the CSRF token and PKCE verifier inside the client to make the auth flow simpler.
• Removed scopes and redirect_uri parameters from Client::from_refresh_token(), as they were pointless.
• Client::shows().get() now returns Vec<Option<SimplifiedShow>>, as the API returns null for some shows
  and the user likely wants to know that some of their shows can't be obtained.
• Made the ExternalIds and ExternalUrls structs' fields public.
• Removed the ability to implement marker traits (such as AuthFlow, Verifier etc.) for library users, using the sealed trait pattern.