Adds upd*Delay functions for tag parser

And a bit of refactoring for updater function names,
they all start with "upd" now.

Signed-off-by: Vlad Velici <vlad.velici@gmail.com>
Tag parser doesn't create empty pointers anymore. Close #35

Except for empty slices, but that should not be
an issue for any writers as
len(nil slice) == len(empty slice) == 0

Signed-off-by: Vlad Velici <vlad.velici@gmail.com>