Make building API docs optional
Make building API docs optional

yusiwen/libmpdclient,sl0th/libmpdclient,jagleeso/libmpdclient,psych0tik/libmpdclient2,jagleeso/libmpdclient,jagleeso/libmpdclient,yusiwen/libmpdclient,cmende/libmpdclient,sl0th/libmpdclient,yusiwen/libmpdclient,sl0th/libmpdclient,jwise/libmpdclient,cmende/libmpdclient,jwise/libmpdclient,cmende/libmpdclient,psych0tik/libmpdclient2,jwise/libmpdclient