When enabled this feature swaps the hash implementation of sha512,
sha256 and ripemd160 for a smaller (but also slower) one.
On embedded processors (Cortex-M4) it can lead to up to a 52% size
reduction, from around 37KiB for just the `process_block` methods of the
three hash functions to 17.8KiB.
We've upgraded MSRV but didn't update clippy config, so some things that
could be improved aren't caught by clippy. This updates the config and
fixes the new issues.
I also `rg '1\.41\.1'`ed for interesting changes and found one
additional improvement.
This is the initial step towards using and maybe enforcing clippy.
It does not fix all lints as some are not applicable. They may be
explicitly ignored later.
Alekos Filini
Martin Habovstiak