Skeleton code for filters.

Skeleton code for filters.

All of the filters specified in RFC4971 9.7.1 through 9.7.5 will
be handled in this loop: comp-filter, prop-filter, param-filter,
is-not-defined, text-match, and probably others as we complete the
spec.

Also, in all of the .c files I unwrapped the license declaration onto a single
line, since the whole thing fits inside 132 characters, and 132 characters is
our official line length now.