Adding project files
Merge branch 'master' of https://github.com/jlalande/undo-redo-example

Conflicts:
	src/main/java/com/jlalande/example/undo_redo/command/AddNumberCommand.java
	src/main/java/com/jlalande/example/undo_redo/command/ClearCommand.java
	src/main/java/com/jlalande/example/undo_redo/service/Calculator.java