add a filter manager

this will allow us to support many arbitrary filters
still need to make all the existing plugins use this framework
add a user-provided void pointer to the filter stucture
switch to using packet state struct to support flowtuple
remove the old filter-ignore flag in prep for adding real filters
switch to using the (as-yet unused) filter framework
bug fixes and error checking for filter framework
update filterbpf to use corsaro_filter framework
extend filter framework to support arbitrary number of filters
filter_init now returns a filter if exists
major rework to filters

renamed filters to tags, re-instated the ignore flag
now plugins have two choices, they can use tags to mark a packet as belonging to some special class,
or they can use the ignore flag to tell successive plugins to ignore this packet, or both.