Record the new Best in the spec and the manual

denoise.md §15: why Best became one network, how it compares with the
mixture and Medium on real photographs and the chart, the candidates that
fell short, the file names, the saved-edit numbering, and the timings on
the 3050 -- 0.51-0.54 s whole-frame, 0.95 s in tiles, against 2.60 s for
the mixture in tiles. The manual lists Bilinear, Fast and Best, says an
edit made with Medium opens with Best, and gives the new time; Medium's
close-up goes.

docs/manual/README.md

@@ -215,22 +215,22 @@ colour that come with it, while keeping the fine detail. Look at it at
 
 `Method` chooses how:
 
-- `Best`, the default: two networks, one for smooth areas and one for
-  edges, blended where each is better. The cleanest skies and the sharpest
-  lettering, and the slowest.
-- `Medium`: one network taught by `Best`. Nearly as clean in smooth areas,
-  a little softer on hard edges, in about a third of the time.
-- `Fast`: a smaller one, taught the same way. Visibly noisier at very high
-  ISO than the other two, but still far cleaner than none, and quick.
+- `Best`, the default: clean skies and sharp lettering, edges kept as
+  crisp as the camera recorded them.
+- `Fast`: a smaller network, taught the same way. Visibly noisier at very
+  high ISO than `Best`, but still far cleaner than none, and quicker.
 - `Bilinear`: the camera's ordinary conversion, noise and all.
 
+A photograph last edited with `Medium`, which earlier versions offered,
+opens with `Best`.
+
 The photograph shows the camera's ordinary conversion while the network
 works, with its progress in the bar at the top, and changes when it is
-done — on a laptop's graphics card, about two and a half seconds for a
-20-megapixel photograph with `Best` and under one with the other two;
-longer on a processor alone or on the tablet. The first photograph after
-installing waits a few minutes more while the graphics card prepares each
-network, once. The result is kept, so a photograph opened again,
+done — on a laptop's graphics card, about a second for a 20-megapixel
+photograph with `Best`, reading the file included; longer on a processor
+alone or on the tablet. After installing, the graphics card spends up to a
+quarter of an hour preparing each network, once, in the background; the
+photographs developed meanwhile take a little longer. The result is kept, so a photograph opened again,
 or exported, does not wait a second time, and switching back to a method
 already used is quick.
 `Strength` eases it off: below 100 % it puts back some of what was removed,
@@ -241,8 +241,8 @@ The lamp and railing of a night frame at ISO 8000, at 1:1, by each method:
 | Bilinear | Fast |
 |---|---|
 | ![The railing and the lamp at ISO 8000, as the camera recorded them](media/develop-denoise-bilinear.png) | ![The same, with the Fast network](media/develop-denoise-fast.png) |
-| **Medium** | **Best** |
-| ![The same, with the Medium network](media/develop-denoise-medium.png) | ![The same, with the Best network](media/develop-denoise-best.png) |
+| **Best** | |
+| ![The same, with the Best network](media/develop-denoise-best.png) | |
 
 It works on raw files from any camera with the usual colour pattern of
 red, green and blue squares — not on JPEGs, and not yet on Fujifilm's