The ASCII writer now supports a filter config option

'only_single_header_row' that turns the output into CSV format.

In that mode all meta data is skipped except for a single header line
with the fields names. Example:

    local my_filter: Log::Filter = [$name = "my-filter", $writer = Log::WRITER_ASCII, $config = table(["only_single_header_row"] = "T")];

Contributed by Carsten Langer.

src/logging/writers/Ascii.h

@@ -45,6 +45,7 @@ private:
 	// Options set from the script-level.
 	bool output_to_stdout;
 	bool include_meta;
+	bool only_single_header_row;
 
 	char* separator;
 	int separator_len;