misc. decision table bugs and improvements

RuleTable and column headers (CONDITION, ACTION,...) are ignored when written with a leading space.
Errors are reported in row & column numbers; this should be done using cell names.
Duplicate columns for rule attributes are silently ignored; there should be a diagnostic.
NumberFormatException thrown on bad integer must be caught and result in a proper diagnostic.
Description entry is notwritten into the generated DRL.
Some attributes cannot be produced: lock-on-active, etc.
NPE thrown for certain entries

Documentation is rather "off" in several places.