Singletons for each reference element type.

This patch implements singleton objects for each reference element type.  At presenent they are read from our "reference_elements/" files, but that does not scale.  My next attempt will be to embed those definitions automatically through static stringstream objects.

This is an incrimental feature to support the following usage:

Elem *phys_elem;

Elem const * ref_elem = phys_elem->reference_elem();

where phys_elem is a typical element and ref_elem is its reference element in parametric coordinates.
shell script to create static reference element strings from files.
include *.data in the source file list
reference element data
implement reference element data
implements reading from static strings rather than file
remove reference to temporary file
fix generated file
remove temporary cruft
newline
return a reference per Roys suggestion
implement missing 1D reference elements
predictable sorting
implement remaining reference elements