* 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()
This macro used to protect the declaration of the [vram] variable of
gint. This variable was short to keep drawing functions short but could
clutter the namespace.
That being said, it's even better to just [#define vram gint_vram] if
you need. This change renames the variable to [gint_vram], exposes it
whenever <gint/display.h> is included, and removes the GINT_NEED_VRAM
macro altogether.
