The former g_BlinkTimer continues running during pauses, and may be used
for more things than just blinks, so it will now be g_Timer.
A previously unidentified variable is a timer which only runs when the
main game is running (when things are unpaused). When loading a save, it
starts as zero. It does not restart when doing things like entering a
new area in the game. This will be called g_GameTimer, since it's the
timer that only runs when in-game. It appears to increment once per
frame.
I have renamed these, changed every instance in which they are used, and
also cleaned up a few instances I found where we had patterns like
`if((variable / value) * value == variable)`, which equates to
`if(variable % value == 0)` which I think makes much more sense. I'm not
sure if I found all those cases, but at least I found a few.
Following up #454 , #453 and related from @sozud , I started to convert
some previously defined headers into proper shared C code. The advantage
from the header is the C file is completely independent, it will have
its own `.data` and `.rodata` and it will be compiled once.
I also took the opportunity to move `include/st/AnimateEntity.h` to
`src/st/animate_entity.h` for consistency. I think the change is small
enough to be included as part of this PR.
