Problem: logs need user-supplied tags for searchability
Problem: logs need user-supplied tags for searchability

Solution: provide hook for short user-specified tag that will be
printed at start of every line. Use fixed width to keep logs clean.

zeromq/zproto,zeromq/zproto,sphaero/zproto,asokoloski/zproto,sappo/zproto,bkmit/zproto,asokoloski/zproto,asokoloski/zproto,hintjens/zproto,somdoron/zproto,jemc/zproto,zeromq/zproto,zeromq/zproto,jdiez17/zproto,hintjens/zproto,sappo/zproto,c-rack/zproto,sphaero/zproto,hintjens/zproto,somdoron/zproto,vyskocilm/zproto,bkmit/zproto,c-rack/zproto,sphaero/zproto,zeromq/zproto,sappo/zproto,asokoloski/zproto,sphaero/zproto,c-rack/zproto,sphaero/zproto,zeromq/zproto,jdiez17/zproto,sphaero/zproto,sappo/zproto,sappo/zproto,vyskocilm/zproto,somdoron/zproto,asokoloski/zproto,hintjens/zproto,jemc/zproto,vyskocilm/zproto,somdoron/zproto,zeromq/zproto,jdiez17/zproto,jdiez17/zproto,jemc/zproto,jdiez17/zproto,hintjens/zproto,somdoron/zproto,c-rack/zproto,somdoron/zproto,jemc/zproto,sappo/zproto,vyskocilm/zproto,jemc/zproto,hintjens/zproto,vyskocilm/zproto,jemc/zproto,c-rack/zproto,bkmit/zproto,hintjens/zproto,bkmit/zproto,asokoloski/zproto,jdiez17/zproto,asokoloski/zproto,vyskocilm/zproto,somdoron/zproto,jemc/zproto,bkmit/zproto,jdiez17/zproto,bkmit/zproto,vyskocilm/zproto,sappo/zproto,c-rack/zproto,c-rack/zproto,bkmit/zproto