haproxy/dev/flags

This needs to be built from the top makefile, for example :

    make dev/flags/flags

Then the executable is usable either one value at a time from the
command line, either with values coming from stdin with "-" passed
alone instead of the value.

It is possible to restrict the decoding to certain fields only by
specifying one of "ana", "chn", "conn", "sc", "si", "sierr", "strm",
"task", or "txn" before the value.