Text.hs: change to use sepSplit

The new sepSplit function can split based on empty lines, so we remove
the hackish text splitting from before and simply use sepSplit. This
is needed as the addition of extra sections would have increased the
code linearly, which we don't want :)

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Balazs Lecz <leczb@google.com>