* Define dgray() to replace gray_start() and gray_stop()
* Introduce a mechanism to override the d*() functions rather than using
another set of functions, namely g*(). Gray rendering should now be
done with d*() (a compatibility macro for g*() is available until v2.1).
* Gray engine now reserves TMU0 at the start of the add-in to prevent
surprises if timers are exhausted, so it nevers fails to start
* Replace other gray engine functions with dgray_*()
* More general rendering functions (in render/) to lessen the burden of
porting them to the gray engine. As a consequence, dtext_opt(),
dprint_opt() and drect_border() are now available in the gray engine,
which was an omission from 230b796.
* Allow C_NONE in more functions, mainly on fx-CG 50
* Remove the now-unused dupdate_noint()
Behave like Basic's Horizontal and Vertical commands. Internal dline()
optimizations are renamed gint_dhline() and gint_dvline().
Also supports ghline() and gvline() in the gray engine.
Optimization cases here are amost negligible due to limiting RAM access
frequencies and the very limited amount of work accomplished in the
functions. Code maintainability is prioritized by using dline().
Lephe
lephe