[make] remove symlinked executables
[git] ignore test trace directory for now
[print] consistent shortform output
[flows] refactor to modules, distinguishing uni- and bi-directional flows
[flows] tweak functional update version
[flows] fully functional updates
[pcap] expose magic_number for writers
[flows] try using mutable state structures

probably slightly more efficient for now; compiler updates in 4.01.0 and
beyond purport to improve it further
[make] add phony setup target
[oasis] refactor to support multiple capture formats
[oasis] consolidate unix apps
[lib] expose more api, rationalise field names
[unix] open right modules for print to build again
[unix] add simplest writer example

`Lwt_cstruct` seems broken, so just use the straight `Unix` module
[lib] add raw `Cstruct.t` to PCAP() tuple
[unix] support new PCAP triple
[unix] first cut at flow splitter

seems ok; but need to do fd management else die with too many open fds