Prepare for 0.4.22 release

[KodrAus]

What's Changed

• Add some clarifications to the library docs by @KodrAus in Add some clarifications to the library docs #620
• Add links to colog crate by @chrivers in Add links to colog crate #621
• adding line_number test + updating some testing infrastructure by @DIvkov575 in adding line_number test + updating some testing infrastructure #619
• Clarify the actual set of functions that can race in _racy variants by @KodrAus in Clarify the actual set of functions that can race in _racy variants #623
• Replace deprecated std::sync::atomic::spin_loop_hint() by @Catamantaloedis in Replace deprecated std::sync::atomic::spin_loop_hint() #625
• Check usage of max_level features by @Thomasdezeeuw in Check usage of max_level features #627
• Remove unneeded import by @Thomasdezeeuw in Remove unneeded import #628
• Loosen orderings for logger initialization in Loosen orderings for logger initialization #632. Originally by @pwoolcoc in Use std::panic::Location to get log location information #599
• Use Location::caller() for file and line info in Use Location::caller() for file and line info #633. Originally by @Cassy343 in Relax atomic orderings #520

[Thomasdezeeuw]

I wasn't able to review this last week, but LGTM except for 1 small thing.

[Thomasdezeeuw]

Nit: missing upper case.