Add sync service

sql/create.sql

@@ -24,7 +24,7 @@ create table if not exists entries(
 	link text not null,
 	date timestamp with time zone not null,
 	content text not null,
-	author text
+	authors text[] not null
 );
 
 create table if not exists entries_users(
@@ -34,6 +34,6 @@ create table if not exists entries_users(
 	is_bookmarked bool not null,
 	is_read_later bool not null,
 	is_ignored bool not null,
-	constraint entries_users_pk primary key(user_id, feed_id)
+	constraint entries_users_pk primary key (user_id, feed_id)
 );