TODO: entity placement
TODO: remembering treasure chests and other progress-related things on revisit. Possibly have events triggered on reentry to a screen segment.

A "page" is a 256-byte block.

map page
    $00..$0F: palette entries
    $10..$11: tile 2K chr bank
    $12..$15: sprite 1K chr bank
    $16: tileset table page
    $17: song number
    $18: width in screens
    $19: height in screens
    $20..$2F: Location name
    $30..$AF: 64-entry zone table (2 bytes little-endian each), indirect jump table for player event handling. (high address of 0 means no event)
first screen page 
    $00..$EF: 16*15 metatile entries
first zone page
    $00..$EF: 16*15 4-bit obs + 4-bit zone
    $F0..$FF: index in map's zone table (0 is the default zone)
second screen page
second zone page
    .
    .
    .
final screen page
final zone page




viewer variables:
camera : (x : word, y : word)
map pointer
tileset pointer