Allow open_browser to be set on creation of auth_manager (SpotifyOAuth/SpotifyPKCE) (#574)

* Fix plamere/spotipy#560

* Adhere to code style

* Update CHANGELOG.md for changes in 939f869bbc

* open_browser passed to get_auth_response should take precedence over the same argument in the constructor

* Update FAQ

* Add information about headless auth

* Add headless auth example

examples/headless.py

@@ -0,0 +1,8 @@
+import spotipy
+
+from spotipy.oauth2 import SpotifyOAuth
+
+# set open_browser=False to prevent Spotipy from attempting to open the default browser
+spotify = spotipy.Spotify(auth_manager=SpotifyOAuth(open_browser=False))
+
+print(spotify.me())