It's a tuple boolean/Match Value - "is it matched?"/"actual match"

Previously effectively agreement was checked on all categories,
even if a lexeme's tag didn't have some of the selected categories.
That led to treating such lexeme as not agreeing with one that had
more matching categories, even if it was agreeing on all categories
that were present.

Underlying issue was temporary table of remaining lexemes for a token not being
updated (emptied) if only underspecified lexemes of the token met an agreement.
Effectively the token was left in its original state i.e. with all
original lexemes present, both those that were underspecified and the remaining
ones that did not met a weak agreement that was otherwise met via the
underspecified lexemes.

So such lexemes are always left in the end.

Intentionally left implicit.

Rule - user-level class encapsulating WCCL rule.
Action - internal class for Rule's actions
ActionExecContext - helper class for execution of actions.

It is coherent now with the SentenceContext::is_inside(int abs_pos)
- SentenceContext::is_inside(Position pos) is added, while
Position::is_inside(SentenceContext) is removed

I.E. empty sentence shouldn't be passed anyway and that is what
Operator class is checking for. But otherwise, at the level of
operator, it can deal with a sentence that has current pos outside
of boundaries.

Previously it would mandate agreement was met on all categories
in a tag with enough categories, if such tag was found.
Now it checks for agreement only on the number of categories that
actually match, including the case of zero categories matching
(the latter does meet the weak agreement).

Clearer and better performing version, also more likely to actually work as expected :)