Line-of-Sight works!  Needs considerable clean-up!

The current implementation does not always produce perfect results
because it uses the center of two endpoint cells as the basis for the DDA
calculations.

Also: This code should be cleaned up to provide better separation between
"grid" or map coordinates and screen coordinates.  Animations, for
example, are generally going to require screen coordinates.  However,
nearly everything else (movement, collision detection, item placement,
etc.) will be based on map coordinates (i.e. in terms of cells, not
pixels.)

Still, this is exciting progress!

Signed-off-by: Atom Macumber <amacumber@eagleproductivity.com>
Implement maximum sight radius for enemies. Crude.

...but it works!  Also added additional enemies back into the test map.
There are now a total of 3 test enemies.

Signed-off-by: Atom Macumber <amacumber@eagleproductivity.com>
Increase enemy sight radius to 20 cells.

Signed-off-by: Atom Macumber <amacumber@eagleproductivity.com>
Clean-up lineOfSight and dda() methods in DDAMap.

Signed-off-by: Atom Macumber <amacumber@eagleproductivity.com>
Add isPassable/containsActor methods to Map.

Also: Update dda.js to use isPassable instead of isCollidable where
appropriate.

Also includes placeholder code for containsItem() method.

Signed-off-by: Atom Macumber <amacumber@eagleproductivity.com>
Add isTransparent method to Map, adjust DDAMap accordingly.

Currently, a cell's transparency is determined by whether or not it is
passable.  This is obviously not a reliable indicator (i.e. deep water)
but since the test map does not contain any data for transparency and
the concept of monster hostility isn't implemented yet, this method will
suffice for the time being.

Signed-off-by: Atom Macumber <amacumber@eagleproductivity.com>
Minor clean-up to game.js.

Signed-off-by: Atom Macumber <amacumber@eagleproductivity.com>
Clean-up/add comments to player.js.

Signed-off-by: Atom Macumber <amacumber@eagleproductivity.com>
Add log to the UI for battle messages, etc.