* WIP premultiplied alpha
* WIP color API rework (doesn't build yet; lots of things left to convert)
* convert everything remaining to new Color api except stage*_event.c files
* convert the stages to new Color api. builds & runs now; still many rendering errors
* fix the bullet shader for premultiplied alpha
* fix masterspark, graphs and stage 1 fog clouds
* fix marisa_b and most of spellcards
* Add deprecation warnings for BLEND_ADD and PFLAG_DRAWADD
* fix a segfault in stage 6
undo accidental earlier change
* fix text_hud.frag.glsl
* fix scuttle bg and remaining stage3 BLEND_ADDs
* fix marisa laser opacity
* hacky fix for myon
The old implementation relied on alpha being stored inside p->color. In
premul alpha this doesn’t work and functions like color_set_opacity
can’t solve this i think.
So I tried messing around with it until it looked somewhat similar.
* fix marisa_b stars
* remove color_set_opacity i overlooked
* more plrmode blending changes
* fixup additive blending in stage 1
* various premultiplied alpha fixups for bosses and enemies
* stage 2 premul alpha fixups
* stage 4 premul alpha fixups
* stage 5 premul alpha fixups
* stage 6 premul alpha fixups
* make lasers also use the PMA blend mode
* remove PFLAG_DRAWADD and PFLAG_DRAWSUB
* fix remaining PMA issues in menus
* lame extraspell bg workaround
* fix item alpha
* make marisaA lasers look somewhat like in master
* fix marisaA bomb background fadeout
* fixup various r_color4 calls
* fix myon
* remove dead code
* fix use of BLEND_ADD in player death effect
* fix myon shot trails (broken on master as well)
* fix myon shot fade-in
* extend the sprite shaders custom parameter to a vec4
* fix youmuB stuff and make it look somewhat better.
the code looks even worse though.
