Start of command hierarchy implementation
#8 Adds extra argument 'String[] args' to execute(...)
#8 Adds extra method 'append(String msg)'
#7 Adds Storage to Location instance
Merge branch 'improve-code' into create-command-hierarchy

Conflicts:
	src/main/java/com/jadventure/game/items/Storage.java
	src/main/java/com/jadventure/game/prompts/CommandCollection.java
	src/main/java/com/jadventure/game/prompts/CommandParser.java
#2 Improve JavaDoc
#9 Implement class execute(...)
#8 Removes output text 'Storage' from visitor
#7 Adds methods:
- public Item getItem(String itemName)
#9 Updates methods:
- public void command_b()
  Replaces original implementation with call to new BackpackCommand