Emulate MDA monocromatic attributes like underline

[MestreLion]

Currently scr_type is hardcoded via #define ROGUE_SCR_TYPE 3, meaning a color, 80x25 adapter. Forcing bw mode in rogue.opt env file screen option works fine, but a bw mode on color hardware is not the same as a "true" mono adapter, and the game distinguishes both cases, as seen by many if scr_type == 7 in the original source. Such "hardware" should be user-selectable at run-time, preferably using a new option in rogue.opt (video_mode perhaps? or, even better, mono_adapter boolean, so columns can be an independent parameter)

On this mode, curses terminal attributes such as A_UNDERLINE should be used, just as seen on true MDA adapters.