add multiple items selection on playlist screen and nested colors support

doc/ncmpcpp_keys

@@ -89,6 +89,10 @@
 #
 #key_lyrics = 'l'
 #
+#key_reverse_selection = 'v'
+#
+#key_deselect_all = 'V'
+#
 #key_clear = 'c'
 #
 #key_crop = 'C'

doc/ncmpcpprc

@@ -70,6 +70,10 @@
 #
 #browser_playlist_prefix = "[red]playlist[/red] "
 #
+#selected_item_prefix = "[magenta]"
+#
+#selected_item_suffix = "[/magenta]"
+#
 ##### various settings #####
 #
 #autocenter_mode = "no"