Move TODO to launchpad.

Update TODO file in the source directory:
 - migrate incomplete items to launchpad
 - remove completed tasks
 - add a reference to launchpad.

TODO

-* ber in lstr
-* handle OOM gracefully
-* link palloc red_zones and check integrety on prelease
-* handle follow failure gracefully
-* add comparer in repo
-* auto tests
-* support cheap palloc_create/palloc_destroy
-* reliable palloc stats (optional verbose)
-* EINTR handling
-* snapshot saving timer
-* remote_hot_standby status - show status 'connection' when connecting
-* rate limit io during dump
-* SEGV
-** with too small arena, when snapshot reading
\ No newline at end of file
+We're using launchpad for tasks tracking and bugs.
+Please use blueprints.launchpad.net/tarantool and
+bugs.launchpad.net/tarantool respectively.
+
+Thank you for your interest in tarantool!