v2.20

        Many improvements from Niels Thykier, hero of the
        free people.  From GH #25:

        * SPEED / INTERNAL: Less time is spent computing prototypes

        * SPEED / INTERNAL: Leak guards are more efficient.

        * SPEED : Expanding tags (eg: qw(:all)) is now faster.
          This also improves the speed of checking autodying
          code with Perl::Critic.

        * INTERNAL: Expanding of tags is faster and preserves order.