make displaying dates of albums in media library optional

doc/config

@@ -302,6 +302,8 @@
 #
 #tag_editor_extended_numeration = "no"
 #
+#media_library_display_date = "yes"
+#
 #enable_window_title = "yes"
 #
 ##

doc/ncmpcpp.1

@@ -255,6 +255,9 @@ If enabled, ncmpcpp will be able to delete directories using its browser screen.
 .B tag_editor_extended_numeration  = yes/no
 If enabled, tag editor will number tracks using format xx/yy (where xx is the current track and yy is total amount of all numbered tracks), not plain xx.
 .TP
+.B media_library_display_date  = yes/no
+If enabled, dates of albums in media library will be displayed and respected in searching, otherwise not.
+.TP
 .B enable_window_title = yes/no
 If enabled, ncmpcpp will override current window title with its own one.
 .TP