Make monsters more three-dimensional; don't crash when they attempt 3D pathing.
New entity pathing system.  Very inefficient right now - it's an extreme rough draft and will improve shortly.
Merge issue
Add monster.cpp back
Make the standard rocky map have much fewer boulders.  Add several new rocky maps.
Add Map::set_movement_map() to make pathfinding faster
Fix an error in rocky.map
Fix some LOS stuff for map.
Prototype for a new entity AI system.
Make docs/ files .txt (see, I'm nice to Windows users!
Add docs/.gitignore to keep txt files in docs
Monster_type (and genus) loads AI.  Includes Entity_AI::opreator=
Remove now-unneeded c_str() from calls to Game::add_msg()
New Map function to get a small Generic_map
Just use a sorted list for Entity_AI's goals - priority numbers don't seem useful and cost us in speed.
Rename AI.txt to ai.txt
New AI system.  It's pretty great!  Will work fine for monsters and NPCs alike.
Purge all references to Intelligence_level since it's obsolete now.  Remove a debug message.
Monsters won't attack monsters within their own genus.
"The zombie hits you for 0 damage" => "The zombie hits you but does no damage"