A compendium is 'a collection of concise but detailed information
about a particular subject'. The Midje compendium contains
the currently relevant facts.

Facts as a data structure

A notation that avoids confusion between what’s essential
about data and what’s accidental. A stand in for constant data.

During checking of a fact, this contains pointers to the facts that contain it,
in outer-to-inner order. The fact itself is the `last` of the sequence.

Maintain the use of namespace-specific prerequisites

What we know about the changing project file/namespace tree.