With the upcoming `#include` cleanup, it finally makes sense to split
off all graphics-related code into its own header. In turn, it makes
more sense to store all of these future master.lib headers in, well,
the master.lib directory, which provides a new 8 characters for their
file names. Turns out that the rationale I gave for the root directory
placement in 8266bbd didn't hold up 3½ years later…
(Also, the `pc98.h` declarations will eventually be split into
`game/coords.hpp` and something in `platform/x86real/pc98/`.)
Part of P0284, funded by [Anonymous] and Blue Bolt.
The .PTN functions, vector functions, and egc_copy_rect_1_to_0_1()
(finally!) from TH01, as well as playfld.hpp from all games(finally!),
together with a bunch of other functions in their vicinity.
Part of P0201, funded by Ember2528 and Yanga.
The .BOS freeing funtions, others that are close to them in the typical
#include order, and the ending picture functions.
Part of P0198, funded by Lmocinemod and Ember2528.
nmlgc