ZeroLog v2

[ltrzesniewski]

I've been working on a v2 of ZeroLog, and I'm currently in that weird no-man's land where I'm not sure if I changed too much or not enough... I's clearly not finished, but I'd like to have your input @rbouallou @MendelMonteiro @rverdier @farnyser about the new design.

Here are the main changes:

General

• ZeroLog now targets .NET 6 only. A netstandard2.0 target needs to be added, which would only allow logging (no appenders, no config, etc).

Loggers

• InfoFormat (etc) methods have been removed, they are replaced by the new interpolated string handlers feature of C# 10 😍, which means the following code:

  _log.Info($"Hello {World()}!");

  is equivalent to:

  if (_log.IsInfoEnabled)
  {
      _log.Info().Append("Hello ").Append(World()).Append("!").Log();
  }

• The ILogEvent interface has been removed, it's replaced by the LogMessage class, in order to remove lots of interface calls.
• The ILog interface has been removed, it's replaced by the Log class, for the same reason. It made sense to have a Log/LogMessage pair of classes. There is now a single implementation instead of 3.
• Calling LogManager.GetLogger before the LogManager is initialized will return a Log object which will work as soon as the log manager is initialized (it previously returned a no-op object which could never work).
• LogEventArgumentExhaustionStrategy has been removed. We now always truncate (it didn't work if the buffer was exceeded previously anyway).

Appenders

• I added a FormattedLogMessage class which represents a formatted message (the logic was in LogManager previously). The IAppender API has been changed to account of this.
• StringFormatter has been removed. The library now uses the built-in features of .NET 6 (ISpanFormattable) that let us format values into a Span<char>. That one required a lot of changes... 😰
• Appenders can now each have a different encoding (makes sense for file vs console for instance).
• The library now allocates a large buffer that will never be extended during formatting (max line size = 16k chars).

TODO

• Validate the new design (this PR)
• Add a limited netstandard2.0 target (logging only)
• I'd like to remove the JSON config, and replace it with something in the code. Also remove the JSON.NET library (a logging library should have no dependencies if possible).
• Appender construction could be better handled (we now supply every parameter separately to the constructor, which makes adding new parameters a breaking change).
• Optimization/benchmarking
• Add more unit tests
• There are still a few TODO comments in the source code
• Truncation support is incomplete right now (it won't truncate value types if string capacity is exceeded)
• Add an interpolated string handler overload to handle .Append($"...")
• DateOnly/TimeOnly
• Ensure a message is not enqueued multiple times
• Strong name
• Update the readme file
• XML documentation
• Test helpers
• Abstract formatting (to support logfmt for instance)