DEV 1761: Add new BoardState and Point fields

[robbles]

The important changes are all here:

rules/board.go

Lines 8 to 28 in a716356

	type BoardState struct {
	Turn int
	Height int
	Width int
	Food []Point
	Snakes []Snake
	Hazards []Point
	// Generic game-level state for maps and rules stages to persist data between turns.
	GameState map[string]string
	// Numeric state keyed to specific points, also persisted between turns.
	PointState map[Point]int
	}
	type Point struct {
	X int `json:"X"`
	Y int `json:"Y"`
	TTL int `json:"TTL,omitempty"`
	Value int `json:"Value,omitempty"`
	}

Nothing is being done with the new fields yet, but they are persisted through cloning of the BoardState.