Subsonic API: extensions WIP

SUBSONIC.md

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+# Subsonic API
+The API version implemented is 1.16.0 and has been tested on _Android_ using _Subsonic Player_, _Ultrasonic_, _Symfonium_, and _DSub_.
+Since _LMS_ uses metadata tags to organize music, a compatibility mode is used to browse the collection when using the directory browsing commands.
+The Subsonic API is enabled by default.
+
+__Note__: since _LMS_ may store hashed and salted passwords or may forward authentication requests to external services, it cannot handle the __token authentication__ method. You may need to check your client to make sure to use the __password__ authentication method.
+
+## OpenSubsonic API
+The following extra fields are implemented:
+* `Album` response:
+  * `musicBrainzId`
+  * `genres`
+  * `artists`
+  * `releaseTypes`
+  * `moods`
+  * `originalReleaseDate`
+  * `isCompilation`
+  * `discTitles`
+* `Child` response:
+  * `musicBrainzId`: note this is actually the recording MBID
+  * `genres`
+  * `artists`
+  * `albumArtists`
+  * `contributors`
+  * `moods`
+  * `replayGain`
+* `Artist` response:
+  * `musicBrainzId`
+  * `sortName`
+  * `roles`
+
+The timeOffset parameter