Deliver an app's saved sends over HTTP, in order and in batches (083)

pure-serve --send OUTPUT=http://host:port/path wires an output: after
every save the owner queues the new sends as JSON (fields and groups)
and a thread per output posts them in order with X-Pure-Source,
X-Pure-Sequence and Idempotency-Key. A 2xx, or a Pure receiver's
refusal, delivers; the owner then trims. 408, 429, 5xx and no answer
are sent again after a pause growing to 10 s, other answers every 10 s:
nothing is dropped. A Pure receiver applies a delivered message with
pure_app_deliver (now taking placed fields) and advertises
X-Pure-Batch: 256; the sender then posts up to that many numbers in a
row as one JSON array (X-Pure-Count), applied in order in one burst
with one save.

Delivery kept up with orders once batched (391 deliveries/s one at a
time; a backlog of 20,000 went at 60k/s). With four clients ordering,
killing the receiver and then the sender (-9) left the receiver's count
and total equal to what the sender saved, five times and under ASan.

1 files changed, 6 insertions, 4 deletions

diff --git a/README.md b/README.md
index 3165850..3108736 100644
--- a/README.md
+++ b/README.md
@@ -6,10 +6,12 @@ in Pure's tree store, every event is a transaction, views are pure functions of
 terminal UI, a CLI, spoken sentences and a web page through [Vega](/srv/git/vega.git), and an HTTP service through
 `pure-serve`: views are GETs and inputs are POSTs, with JSON bodies (groups included) read in place; answers are
 durable, a commit being one contiguous write and one sync; views are read from a snapshot of the last save, so
-reads never wait for a sync. Measurements against axum and drogon on a Raspberry Pi 5 are in
-[075](docs/research/075-http-host-against-axum.md), [077](docs/research/077-apps-as-http-services.md),
-[080](docs/research/080-snapshot-reads.md), [081](docs/research/081-tail-records.md) and
-[082](docs/research/082-json-in-place.md); the status table is [CHECKPOINT.md](CHECKPOINT.md). The text below
+reads never wait for a sync. What an app sends is saved with its event and delivered over HTTP in order and in
+batches, and a receiving app applies each message once. Measurements against axum and drogon on a Raspberry Pi 5
+are in [075](docs/research/075-http-host-against-axum.md), [077](docs/research/077-apps-as-http-services.md),
+[080](docs/research/080-snapshot-reads.md), [081](docs/research/081-tail-records.md),
+[082](docs/research/082-json-in-place.md) and [083](docs/research/083-delivery-over-http.md); the status table is
+[CHECKPOINT.md](CHECKPOINT.md). The text below
 records the earlier document runtime this grew from.
 
 A standalone native micro runtime being designed as a small operating