Added cache handler to SpotifyClientCredentials and fixed a bug in refresh tokens methods that raised the wrong exception (#655)

* Added an exception clause that catches `FileNotFoundError` and logs a debug message in `SpotifyOAuth.get_cached_token`, `SpotifyPKCE.get_cached_token` and `SpotifyImplicitGrant.get_cached_token`.

* Changed docs for `auth` parameter of `Spotify.init` to `access token` instead of `authorization token`. In issue #599, a user confused the access token with the authorization code.

* Updated CHANGELOG.md

* Removed `FileNotFoundError` because it does not exist in python 2.7 (*sigh*) and replaced it with a call to `os.path.exists`.

* Replaced ` os.path.exists` with `error.errno == errno.ENOENT` to supress errors when the cache file does not exist.

* Changed docs for `search` to mention that you can provide multiple multiple types to search for. The query parameters of requests are now logged. Added log messages for when the access token and refresh tokens are retrieved and when they are refreshed. Other small grammar fixes.

* Removed duplicate word "multiple" from CHANGELOG

* * Fixed the bugs in `SpotifyOAuth.refresh_access_token` and `SpotifyPKCE.refresh_access_token` which raised the incorrect exception upon receiving an error response from the server. This addresses #645.
* Fixed a bug in `RequestHandler.do_GET` in which the non-existent `state` attribute of  `SpotifyOauthError` is accessed. This bug occurs when the user clicks "cancel" in the permissions dialog that opens in the browser.
* Cleaned up the documentation for `SpotifyClientCredentials.__init__`, `SpotifyOAuth.__init__`, and `SpotifyPKCE.__init__`.

* Removed unneeded import

Co-authored-by: Stéphane Bruckert <stephane.bruckert@gmail.com>

CHANGELOG.md

@@ -5,15 +5,27 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-
 ## Unreleased
 
 ### Added
+
 - Enabled using both short and long IDs for playlist_change_details
+- Added a cache handler to `SpotifyClientCredentials`
 
 ### Changed
+
 - Add support for a list of scopes rather than just a comma separated string of scopes
 
+### Fixed
+
+* Fixed the bugs in `SpotifyOAuth.refresh_access_token` and `SpotifyPKCE.refresh_access_token` which raised the incorrect exception upon receiving an error response from the server. This addresses #645.
+
+* Fixed a bug in `RequestHandler.do_GET` in which the non-existent `state` attribute of  `SpotifyOauthError` is accessed. This bug occurs when the user clicks "cancel" in the permissions dialog that opens in the browser.
+
+* Cleaned up the documentation for `SpotifyClientCredentials.__init__`, `SpotifyOAuth.__init__`, and `SpotifyPKCE.__init__`.
+
+    
+
 ## [2.17.1] - 2021-02-28
 
 ### Fixed