Moving ephemerals into the core.  Using them as a weak table to store filenos,
and enforcing the invariant that there is only one fileno object with a given
number at a time.
Using a hash for the fileno table.
Adding an optional count arg to regexp-replace to replace just the nth match.
If we lookup a fileno that was cached but closed we need to reopen it.
Updating regexp-match-num-matches to SRFI 115 regexp-match-count.
Adding maybe-gunzip utility for optionally compressed inputs.
Adding http-get-to-file utility.