Added JavaDoc, sorta fixed nodeAt
Merge branch 'master' into jimmy

Conflicts:
	src/ast/Command.java
	src/ast/ExpressionImpl.java
	src/ast/Factor.java
	src/ast/Number.java
	src/ast/Relation.java
	src/ast/Sensor.java
	src/ast/UpdateOrAction.java

Finally merged the files.  Now I can do a pull request.