Adds a new eprintln_locked macro which locks STDOUT before logging
to STDERR. This patch also replaces instances of eprintln with
eprintln_locked to avoid interleaving lines.
Fixes#1941, Closes#1968
The top-level listing was just getting a bit too long for my taste. So
put all of the code in one directory and shrink the large top-level mess
to a small top-level mess.
NOTE: This commit only contains renames. The subsequent commit will
actually make ripgrep build again. We do it this way with the naive hope
that this will make it easier for git history to track the renames.
Sigh.
