Prolog interface has [en|dis]able_regression/1 predicates.

Removed entailsreg/3.
Setup::AddClause() takes over the task of Setup::AddSensingResult().

With regression, adding a sensing result boils down to adding several
clauses which are the result of first regressing the SF literal and
converting the result to CNF.
That's obviously a task for Setup::AddClause(), not for
Setup::AddSensingResult().

To fulfill this task, Setup::AddClause() needs to perform the
consistency checks similar to the one performed by
Setup::AddSensingResult(). In fact, the newly added clause made things
inconsistent at level k if at for all literals from their clause, the
flipped literal is entailed at level k.

Like in Setup::AddSensingResult(), the consistency check is performed
only for those k for which there are entries in incons_. Since incons_
is empty initially when the setup is filled with clauses, the new
Setup::AddClause() has no overhead over the old version for the
traditional use case of filling the setup.

Setups::AddClause() forwards to Setup::AddClause() as before.

Removed Setup[s]::AddSensingResult() because it's subsumed by
Setup[s]::AddClause() now.
Box clauses are not instantiated for {} and added immediately.

When we're doing regression, this just pollutes the setup.
When we're not doing regression, the purpose was just to get the names
of the clause into hplus. That can be achieved with UpdateHPlusFor just
as well.
Added SfLiteral subclass.

A more convenient way to create SF literals.
Updated examples to use [en|dis]able_regression/1.

All of that in single files. See each file for how to en/disable regression.