Update documentation to reflect recent changes

[samuelmurray]

Update documentation to reflect recent changes

Motivation:

The documentation was not updated in SLG-0003 or SLG-0005. Concretely, the examples given in the documentation used the now deprecated multiparameter methods in LogHandler, and the new LogEvent-based method were not listed among the others. Likewise, the new logging methods (Logger.trace etc.) that take an Error as a parameter were not added. Lastly, LogEvent had no separate entry.
While the default rendered docs for these were acceptable, it decreased the discoverability of the new methods, and the examples using deprecated methods were misleading.

Modifications:

• Update all code examples to use non-deprecated methods.
• List all new methods on Logger and LogHandler along the existing ones.
• Add a minimal file for LogEvent to give it the same look as all other types.
• Update code examples in .md files to follow swift format.

Result:

Documentation reflects the current state and best practices of swift-log.

[kukushechkin]

Thanks for this documentation update, @samuelmurray!

[heckj]

An additional thank you @samuelmurray - on top of @kukushechkin ! Appreciate you taking the time with this!

[kukushechkin]

FYI, the CI is in shambles (not only in this repo), there is nothing wrong with the PR.

[samuelmurray]

After looking at the documentation at swiftpackageindex, I realised that the InMemoryLogging target is missing. When building the documentation in Xcode, I get both target, but perhaps swiftpackageindex requires a .docc catalog?
Anyway, I could add a minimal documentation for that target as well, either in this PR or in a separate one.