Mission.hh: fully document unit.
Base.hh: finish documenting unit.
Doxyfile: expand t1only/t2only aliases and disable INLINE_INFO.

DifficultyMessage: use name test instead of type test for wrapper ctor.

AmbientLightZone, EnvironmentMapZone: remove largely pointless enums.
Room: convert ambient_light_zone and environment_map_zone to unsigned (from removed enum types).

Mission: rename show_movie method to show_video.