* Switch to crossbeam-channel + rayon::spawn
* Remove thread_spawn for evaluation altogether
This allows to avoid a deadlock when there is only one Rayon thread, and doesn't sacrifice performance, since the caller of .get_result() had to always block on the iterator to be finished anyway, and all the messages are already sent from separate threads.
* Fix `verbose_mode` test
This one is easier to "fix", since we're in control of the rayon pool - just adding one extra thread to the default number to make sure we always can one root "spawn" call without stealing from the actual pool.
This allows to configure or compile away logging in the library from a single place in Rust apps.
For the CLI side, the usage and output remained the same, except it's now colour-coded.
Fixes#217.
* Improve performance consistency
Switch from HashMap / HashSet to IndexMap / IndexSet for consistent iteration order of various options and, as a result, more predictable performance.
libdeflater is a Rust wrapper around
[libdeflate](https://github.com/ebiggers/libdeflate) - an alternative
heavily optimised library for deflate/zlib/gzip compression and
decompression that is intended for situations where upper bounds of the
output are well-known.
In my benchmarks on test files in the repo it has shown to be usually
both slightly faster and providing better compressed output than
cloudflare-zlib, but in some cases showing the opposite, so rather
than swapping defaults, it's currently provided as another option,
similarly to zopfli.
Since it's not strictly better in all cases, I'm not providing median
numbers, but you can check distribution histograms for time and size
differences here (all using `oxipng -o 6 -t 6 -P`):
https://docs.google.com/spreadsheets/d/1WOKgeYZBhLkQvMGAC36snN4azilElzOFhx63RJu0EZY/edit?usp=sharing
* Fix verbose message
* No cloning when restoring original data
* Make reductions return a new uncompressed image
Partially fixes#145
* Async reduction evaluator
* Assert
* Faster bit depth check
* Also try 4-bit depth for small-depth images
* Skip test when using miniz
* Ensure palette is trimmed after depth reduction
Fixes#159
* Fudge factor for reductions to prefer better reductions even if gzip estimation says otherwise
