Update and optimize dependencies (#445)

* Update and optimize dependencies

These changes update the dependencies to their latest versions, fixing
some known issues that prevented doing so in the first place.

In addition, the direct dependency on byteorder was dropped in favor
of stdlib functions that have been stabilized for some time in Rust, and
the transitive dependency on chrono, pulled by stderrlog, was also
dropped, which had been affected by security issues and improperly
maintained in the past:

- cardoe/stderrlog-rs#31
- https://www.reddit.com/r/rust/comments/ts84n4/chrono_or_time_03/

* Run rustfmt

* Bump MSRV to 1.56.1

Updating to this patch version should not be cumbersome for end-users,
and it is required by a transitive dependency.

* Bump MSRV to 1.57.0

os_str_bytes requires it.

.github/workflows/oxipng.yml

@@ -19,7 +19,7 @@ jobs:
           - x86_64-apple-darwin
         toolchain:
           # Minimum stable
-          - "1.56.0"
+          - "1.57.0"
           - stable
           - beta
           - nightly