Split PTS.Syntax.AST.
Format list of exposed modules.

The list is now ordered alphabetically. List items are no longer
separated by commas to reduce diff noise when adding at the end
of the list.
Reorganize module hierarchy PTS.Dynamics.*.

The new module PTS.Dynamics exports everything the other modules of the
system need to know about the dynamic semantics of PTS programs,
including the Value type and support for evaluation, reification,
Normalization and  comparision of values. These features are implemented
in the modules of the PTS.Dynamics.* hierarchy.
Reorganize module hierarchy PTS.Statics.*.

The new module PTS.Statics exports everything the other modules of the
system need to know about the static semantics of PTS programs,
including support for type checking. These features are implemented
in the modules of the PTS.Statics.* hierarchy.
Delete unused files.