Most work is now done by instances generator when it is run (that is
when compiling DIVINE). Contrary to situation with old automatic instantiation,
the select function is now also auto generated, therefore the run-time overhead
of instantiation should be less then or equal to previous version.

There are still things this are probably outdated though.

Now:
- for each list of possible component values, it is specified whether
there is default value (last) and whether user should be warned if selection
of one components shadows others (such as POR vs. fairness for DVE).
- user is warned is component would be selected but is is not compiled in
(such as POR when compiled with O_SMALL, or missing generator)

The Trait helper class is introduced in definitions.h, it defines boolean
attributes which respects to compile-time options (such as O_COMPRESSION).

The instance of this class specifiing what is compiled-in can be obtained
by calling Traits::compiled().

Traits can be then used to specify when will instance be generated, atomic traits
are given by pointer-to-member of Traits structure which specifies if feature
is enabled (or by pointer-to-member-function-returning-bool). Those atomic
traits are wrapped in Traits::Get object, to became traits. Traits can be combined
using logincal operations !, && and || (see for example traits for Mpi topology).

It was previously in instances/definition.h.

And allow readig it even if DIVINE is not compiled with O_EXPLICIT.