DEV 1247: Add a new map generator interface (#71)

* reorganize code

* first draft of map generator interfaces

* add explicit random interface to board helpers

* implement standard map

* rename Generator to GameMap

* allow initializing snakes separately from placing them

* add random number generator to Settings

* updates to GameMap interface

* add helpers for creating and updating BoardState with maps

maps/helpers.go

@@ -0,0 +1,42 @@
+package maps
+
+import "github.com/BattlesnakeOfficial/rules"
+
+// SetupBoard is a shortcut for looking up a map by ID and initializing a new board state with it.
+func SetupBoard(mapID string, settings rules.Settings, width, height int, snakeIDs []string) (*rules.BoardState, error) {
+	boardState := rules.NewBoardState(int32(width), int32(height))
+
+	rules.InitializeSnakes(boardState, snakeIDs)
+
+	gameMap, err := GetMap(mapID)
+	if err != nil {
+		return nil, err
+	}
+
+	editor := NewBoardStateEditor(boardState, settings.Rand())
+
+	err = gameMap.SetupBoard(boardState, settings, editor)
+	if err != nil {
+		return nil, err
+	}
+
+	return boardState, nil
+}
+
+//  UpdateBoard is a shortcut for looking up a map by ID and updating an existing board state with it.
+func UpdateBoard(mapID string, previousBoardState *rules.BoardState, settings rules.Settings) (*rules.BoardState, error) {
+	gameMap, err := GetMap(mapID)
+	if err != nil {
+		return nil, err
+	}
+
+	nextBoardState := previousBoardState.Clone()
+	editor := NewBoardStateEditor(nextBoardState, settings.Rand())
+
+	err = gameMap.SetupBoard(previousBoardState, settings, editor)
+	if err != nil {
+		return nil, err
+	}
+
+	return nextBoardState, nil
+}