Generate a log-file in orgdown format

[novoid]

Additionally to the stdout messages, a log file is generated in orgdown format:

• config entry for the path in config.py: no path = same path as lazyblorg binary; absolute path = absolute path (what did you think?)
• log file is generated as temp file (same path as target log file but with different extension/ending); only when whole process is finished without error, the previous log file is replaced with the new (temporary) one so that only full run logfiles reside
• list of hidden articles in one heading that has tag "noexport" so that log file might be part of the lazyblorg blog files to publish
  • would require more config options such as setting an ID, further tags, and so forth -> log as github issue for future idea
• top element = list with major workflow
• a separate table with the duration of each major workflow step
• include statistics (similar to stdout nowadays: num of headings, types of pages, ...)