Implemented:
* basic features for logging with severity levels
* lexically scoped properties
* dynamically scoped properties
* 3 output formats (textline, textblock and json)
* optional timestamps
To-do:
* compile-time filtering of certaiin topics and severity
levels (potentially removing all logging)
* optional run-time filtering
* specification of the log outputs/formats through a define
* colorful output in the terminal
* documentation
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