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* New keyword 'filename_sub_re', using regex to substitute filename substrings.
* Renamed 'filename_substitution' keyword to 'filename_sub'.
* filename_sub (and filename_sub_re) now support more than two elements, FIND1, REPLACE1, FIND2, REPLACE2, etc.
* removed lines_commentmidchar keyword, should just use lines_commentchar consistently.
* Parsing command line args before loading system config, passing config_app_defaults to parser instead.
* Properly removing load_system_config and stdout/stderr/etc from config.
* Updated command line args help and metavars
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