This also includes an example for generating a quad primitive. In
flycast, this is very obviously rendered as two triangles. On real
hardware, this appears to be a "native" quad.
This rearranges scene.cpp to a file organization that more closely
follows which code is responsible for what area of (hardware)
initialization.
All TA and CORE register accesses now use the new ta_bits.h and
core_bits.h, respectively.
