Break Game constructor into more functions

[juniper-wright]

The Game constructor has four distinct parts:

1.) Parsing the parameters on the Game node.

2.) Parsing the nodes in the Commands node.

3.) Parsing the nodes in the Items node.

4.) Parsing the nodes in the Rooms node.

Each of parts 2-4 should have its own function.

Proposition:

private void buildGameCommands(Node commandsNode) { }
private void buildGameItems(Node itemsNode) { }
private void buildGameRooms(Node roomsNode) { }

[juniper-wright]

Resolved by resolution of #31, #32, and #33.