[lbrainz] Add ListenBrainz integration

- Support submitting listens (scrobble) to ListenBrainz.
- Add JSON API endpoints to manage ListenBrainz auth token.

src/listenbrainz.h

@@ -0,0 +1,25 @@
+
+#ifndef __LISTENBRAINZ_H__
+#define __LISTENBRAINZ_H__
+
+struct listenbrainz_status {
+  bool disabled;
+  char *user_name;
+  bool token_valid;
+  char *message;
+};
+
+int
+listenbrainz_scrobble(int mfi_id);
+int
+listenbrainz_token_set(const char *token);
+int
+listenbrainz_token_delete(void);
+int
+listenbrainz_status_get(struct listenbrainz_status *status);
+void
+listenbrainz_status_free(struct listenbrainz_status *status, bool content_only);
+int
+listenbrainz_init(void);
+
+#endif /* !__LISTENBRAINZ_H__ */