An interface for getting a character's destination x/y

This adds Character::DestinationX and Character::DestinationY. Two
read-only properties that can be used to determine where a character is
heading while that character is moving. Returns the character's current
position if the character isn't moving. This seemed sensible to me.
Merge pull request #20 from gurok/bugtracker_get_walk_destination

An interface for getting a character's destination x/y