The "defer" environment has been replaced with three environments
"rationale", "testing" and "implement" that ship the enclosed text
to a r-, t-, and i- support file.

The .rat files are no more are now .sub files.

Two new cross reference commands have been introduced \tref and
\iref.  They work in precisely the same way as the existing \rref
but refer to the test and imp namespaces respectfully.

Two new macros \test{}{} and \ftest{}{}{} have been defined for
the test cases.