Fix memory leak.
Fix bug in PCAP sink.

When dumping packets, both "len" and "caplen" need to have the same size.
Otherwise ::pcap_dump will segfault sporadically.

VAST now has the key Time Machine functionality in place: indexing the
connection 4-tuple (without the payload, per #52), bidirectional cutoff, and
writing PCAP traces based on query results.

Closes #51.
Simplify README.