docs: Add Code-ref section.

* Improve installation guide.
* Remove @author from file-headers.
excel: FIX Excel-refs parsing when miss sheet_name.

** FIX bug also in **kws.
** tests: Add test for excel-xwings.
** docs: Add BNF syntax.
* cmd, log: Remove extra notice-level, use 'trace' instead.	
* pdcalc: BUG DISCOVERED in cyclic-deps but feasible calc.