v0.22.0

The image set: QOI, Netpbm, TGA, ICO and CUR, and TIFF, each reaching
every other image format, with an area-averaging downscale for icons;
a faster PNG reader that also reads the highly compressed chunks it
refused since 0.19.0; and deflate that stops searching on noise.

Fixed

• A PNG whose small image data inflates far past the reader's step (a 1.2 KB chunk holding a 256 KB image, as Pillow writes flat icons) is read whole; the reader stopped when the chunk's bytes were used up, with output still inside the inflater, and called it cut short. In every release since 0.19.0.

Added

• TIFF both ways (src/io/tiff.rs): the first page read from strips or tiles, chunky or planar, uncompressed, LZW, deflate, or PackBits, with the horizontal predictor, at 1 to 16 bits in gray, palette, RGB, or CMYK with either kind of alpha; written as 8-bit deflate strips with the predictor. Pair tiff-png against the image and tiff crates. Map in DOCS/formats/tiff.md.
• ICO both ways and CUR read (src/io/ico.rs): the largest, deepest entry read from PNG or BMP entries (AND masks, alpha-less 32-bit entries as Windows reads them); icons written with the standard sizes that fit, the source itself as the largest when it fits in 256, from one streaming downscale. Pair ico-png against the image crate. Map in DOCS/formats/ico.md.
• An area-averaging downscale (src/image/resize.rs) that streams source rows and weights color by alpha.
• TGA both ways (src/io/tga.rs): every common layout read (color-mapped, truecolor, gray; raw and RLE; 15 to 32 bits; both orientations), top-down RLE written as Pillow writes it; a bottom-up file holds its bytes, not its pixels. Pair tga-png against the image and png crates. Map in DOCS/formats/tga.md.
• Netpbm (src/io/netpbm.rs): PBM, PGM, PPM in plain and raw forms and PAM, one streaming reader for every form and a writer for each kind, to and from every image format. Pair ppm-png against the image and png crates. Map in DOCS/formats/netpbm.md.
• QOI both ways (src/io/qoi.rs): a streaming reader and a writer that produces qoi.h's bytes, to and from every image format. Pair qoi-png against the qoi and png crates. Map in DOCS/formats/qoi.md.

Changed

• The binary size budget is raised 2.25 -> 2.40 MB and the WebAssembly budget 1.10 -> 1.20 MB for the 0.22 image formats (QOI, Netpbm, TGA, ICO, the downscale, and TIFF to come).
• Deflate on noise searches one position in eight and writes the rest as literals (literals are what pays there): a noisy photograph's PNG writes in 40% of the time and a little smaller; the lossless WebP photo decode goes from 53 to 93 MB/s.
• The benchmark harness removes an out-* output before each timed run, so both sides write a fresh file (a rename over an existing file costs a writeback on btrfs and ext4 that a truncate does not).
• The PNG reader relies on each chunk's CRC-32 and no longer sums Adler-32 over the decoded data (the png crate skips it by default too): 7% faster on a large photo, 20% on flat images.
• Image pairs are generated from one table of codecs, each saying what its reader and its writer lose: every reader reaches every writer, and each pair's fidelity carries both texts (a new raster format is one table row).