Keep the bans, the clients and GeoJS's answers in state files (closes #17)

smallwebwaf now copies its state to bans.json, clients.json and
lookups.json in SWWAF_STATE_DIR, as "Persistent state" in SPEC.md
describes, and reads them back at start, so a restart lifts no ban and
gives no client a fresh allowance. Each client gains a history, and a
ban's notes count the netblock's requests. bans.json is written
SWWAF_STATE_WRITE_DELAY after a ban, every file every
SWWAF_STATE_COUNTER_INTERVAL and at the stop, each through a synced
temporary file renamed over it. A file that does not parse, an unknown
version or an unwritable directory stops the start. The image gets
/var/lib/smallwebwaf, which the run script gives to the smallwebwaf user.

Deviation: no AS number or name, and no ban cause, reason or lifting yet.

Model: opus-5-5

script/run

@@ -1,6 +1,7 @@
 #!/bin/sh
 # script/run: build bin/smallwebwaf with script/build and run it, with
-# the settings in the environment.
+# the settings in the environment. Unless SWWAF_STATE_DIR is set, the
+# state files go in bin/state, beside the binary.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
@@ -8,6 +9,11 @@ ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     "$SCRIPT_DIR/build"
+    if [ -z "${SWWAF_STATE_DIR+set}" ]; then
+        SWWAF_STATE_DIR="$ROOT/bin/state"
+        export SWWAF_STATE_DIR
+        mkdir -p "$SWWAF_STATE_DIR"
+    fi
     exec "$ROOT/bin/smallwebwaf"
 }