Implement Doug's two killer features: 1) store all occurrences of a

Implement Doug's two killer features: 1) store all occurrences of a
header, not just the last, 2) use pure ordered structure for the
filters, allowing inter-mixing of filters (i.e. you can have some
List-Id filters followed by some X-Mailing-List filters followed by
more List-Id filters and they will all be matched in the correct
order).

Earlier i was using Tie::IxHash to make the filters hash ordered, but
i wasn't using it for the internal hashes so it was incomplete.  I
didn't need hashes in teh first place; switching to nested arrays for
the filters structure solves this problem as well as Doug's killer
feature and as a bonus removes the Tie::IxHash dependency.

README:
    Remove Tie::IxHash from list of non-standard modules.

minc:
    Drop Tie::IxHash.

    FILTERS and %headers become more complex structures (code and
    documentation changes).

    For now, use .mincfilter2 instead of .mincfilter (will change
    back as soon as the new code has had a good shake-down).

    (log_headers): Adapt for new %headers structure and add comment
    cross-referencing the get_headers comment explaining the
    structure.

    (get_headers): Document the %headers structure.  Build and return
    the new structure, preserving multiple occurrences of the same
    header.

    (find_mh_folder): Use the new @FILTERS structure.

    (MAIN): Use @FILTERS instead of %FILTERS.

    In the closing pod section, fix the EXAMPLES section and add a
    section documenting @FILTERS.