Major update: Fix bug in XTMUNIT so that SETUP and TEARDOWN are ran

before and after each test rather than only once. STARTUP and SHUTDOWN already
exist to run something only once.

Some refactoring of code in XTMUNIT was done as well where some methods were
moved over to the routine XTMUNIT1 to keep the code in XTMUNIT clean.

New kids file T13. KIDS file includes descriptions now.

Tiny fix to XT_7.3_81 M-UNIT tests, XTMRPRNT, M-Unit GUI.txt to say that
@TEST is now supported. Example changed to include @TEST.