Update map description document

Additions:

 - property description standard for tiles to be implemented here on out

Changes:

 - beacons should now just turn on the light in all four directions
   rather than cycle through each direction.  This decision was made
   partially in deference to the logic design, but it also simplifies a
   needless complication of game-play.

Aesthetic changes:

 - document is now diff-friendly
 - added document meta-data