add support for enclosures (closes #165)

schema/ttrss_schema_mysql.sql

@@ -209,6 +209,7 @@ create table ttrss_enclosures (id serial not null primary key,
 	content_type varchar(250) not null,
 	post_id integer not null,
 	title text not null,
+	duration text not null,
 	index (post_id),
 	foreign key (post_id) references ttrss_entries(id) ON DELETE cascade);