Add the beginnings of a generic prompt system, with exclusive support
atm for string prompts, and test it out by asking the character for
their name at startup
As the character walks around the map, progressively reveal the entities
on the map to them, using an algorithm based on well known
circle-rasterizing and line-rasterizing algorithms to calculate lines of
sight that are potentially obscured by walls.
Add support for converting generated levels to walls, and merge one into
the entity map at the beginning of the game.
There's nothing here that guarantees the character ends up *inside* the
level though (they almost always don't) so that'll have to be slotted
into the level generation process.
