Improve the test coverage

[BurningEnlightenment]

Extend the test suite to the point where code changes can be committed with general confidence in their soundness.

Tasks

• Write integration tests covering the common usage scenarios.
• Write comprehensive tests for the log macros.
• Write tests for the log clock time conversion functions.
• Write comprehensive tests for the file database implementation.
• Write tests for the attribute transmorpher.
• Write tests for the argument transmorpher.
• Write comprehensive tests for the log source API
• Write comprehensive tests for the log sink API and its implementations
• Write tests for the file_stream classes.
• Write tests for the interleaving stream classes.
• Migrate existing tests from Boost.Test to Catch2 #15