Log the start-up checkpoint's figures under their own names (closes #117)

Initialize scanned the row of PRAGMA wal_checkpoint(TRUNCATE), which is
the busy flag, the frames in the WAL and the frames copied, into
wal_pages, checkpointed and moved; and a completed TRUNCATE reads 0 for
both counts. The line now logs busy, wal_frames and checkpointed_frames,
plus wal_bytes, the WAL file's size, which New reads before it opens the
database because the open writes a frame to the WAL. The line is a
warning when busy is 1. Tests open a database a second time while the
first stays open, with and without a read open on the first, and check
the line's level and figures.

Model: opus-5-5

README.md

@@ -5,22 +5,6 @@ table in real time: it streams BGP UPDATE messages from the RIPE RIS Live
 service, maintains a live routing table in SQLite, and provides HTTP APIs for
 querying routing information.
 
-## Rationale
-
-RIPE RIS Live streams the BGP updates that RIPE's route collectors receive, as
-they happen, from the moment a client connects. It reports changes, not the
-routing table they add up to, so it cannot say which AS an IP address is routed
-to now or which routes a prefix has. RouteWatch applies the feed's updates to
-live routing tables in its own SQLite database and answers IP-to-AS lookups and
-prefix pages from them.
-
-The feed sends no table when a client connects, so these tables hold only the
-routes the feed has announced since RouteWatch first started: an IP-to-AS lookup
-finds nothing for an address whose routes have not been announced since then.
-The tables also miss the updates RouteWatch drops when it falls behind under
-load and those sent while it is stopped, so a lookup or a prefix page can show a
-route the feed has withdrawn.
-
 ## Features
 
 - Real-time streaming of BGP updates from RIPE RIS Live