* Fix bKGD conversion from gray to palette
* Allow grayscale reduction from 16 to 4 or less
* Refactor reduction evaluation sequence
* Separate palette into new file
* Refactor ColorType
Move transparency and palette data into the ColorType
* Fixup tests
* Make more use of helper functions
* Change BitDepth to u8 representation with TryFrom
* Fix clippy lints
* Don't use unstable language features
* Restore documentation on transparency/palette
* add `workflow_dispatch` for manual running
* add `fail-fast` false in matrix
* specify `persist-credentials: false` for actions/checkout
* update actions to the latest versions
* move cache before installing the toolchain
* cache more stuff
* limit deploy to shssoichiro/oxipng repository
* reindent
* Make dependency on `image` optional
After PR https://github.com/shssoichiro/oxipng/pull/481 was merged, the
`image` dependency became unused when building with debug assertions
disabled, as it is only used to implement output sanity checks when such
assertions are enabled.
The `image` crate transitively pulls a significant amount of
dependencies, so it's useful for OxiPNG users to get rid of them when
not needed.
[Cargo does not allow specifying dependencies that are only pulled when
debug assertions are
enabled](https://github.com/rust-lang/cargo/issues/7634), so the next
best way to give users some flexibility is to gate those debug
assertions behind a feature flag.
These changes add a `sanity-checks` feature flag that controls whether
the `image` crate and the related sanity checks are compiled in. This
feature is enabled by default to keep debug builds useful to catch
problems during development.
* Fix Clippy lints
* Run tests with new sanity-checks feature enabled
`crossbeam-channel` is only used if the `parallel` flag is enabled, so
it can be gated behind that feature flag to potentially reduce the size
of the build dependency tree for dependent projects.
While at it, I've fixed several warnings emmitted in tests/flags.rs.
The `itertools` dependency became unused at a3b104a2ed, so there is no point in declaring it as a dependency any longer.
This was detected with the help of the
[`cargo-udeps`](https://github.com/est31/cargo-udeps) tool. I then
verified that it was not a false positive.
* Refactor filters as enum
* Include filter byte in filter output
* Add entropy filter
* Add bigrams filter
* Add bigram entropy filter
* Add brute filter
* Replace bit-vec
* Add tests and benches
* Show filters in help
* Use FxHasher in color to palette
* Use windows function for minor improvement
* Switch main compressor to libdeflate
* Use libdeflater in evaluate
* Use libdeflater to inflate
* Use libdeflater crc
* Tidy up
* Fix benches
* Allow libdeflater/freestanding feature
* Fix building without zopfli
