fix TODOs #22
Description
:checkstyleMain[ant:checkstyle] [INFO] /home/gradle/src/main/java/io/github/marioluan/datastructures/Node.java:16:14: Variable 'data' must be private and have accessor methods. [VisibilityModifier]
[ant:checkstyle] [INFO] /home/gradle/src/main/java/io/github/marioluan/datastructures/Node.java:21:20: Variable 'next' must be private and have accessor methods. [VisibilityModifier]
[ant:checkstyle] [INFO] /home/gradle/src/main/java/io/github/marioluan/datastructures/Node.java:26:20: Variable 'prev' must be private and have accessor methods. [VisibilityModifier]
[ant:checkstyle] [INFO] /home/gradle/src/main/java/io/github/marioluan/datastructures/graph/Digraph.java:55: Comment matches to-do format 'TODO'. [TodoComment]
[ant:checkstyle] [INFO] /home/gradle/src/main/java/io/github/marioluan/datastructures/graph/Undirected.java:56: Comment matches to-do format 'TODO'. [TodoComment]
[ant:checkstyle] [INFO] /home/gradle/src/main/java/io/github/marioluan/datastructures/graph/search/BreadthFirstSearch.java:34: Comment matches to-do format 'TODO'. [TodoComment]
[ant:checkstyle] [INFO] /home/gradle/src/main/java/io/github/marioluan/datastructures/graph/search/ConnectedComponents.java:43: Comment matches to-do format 'TODO'. [TodoComment]
[ant:checkstyle] [INFO] /home/gradle/src/main/java/io/github/marioluan/datastructures/graph/search/Paths.java:25: Comment matches to-do format 'TODO'. [TodoComment]
[ant:checkstyle] [INFO] /home/gradle/src/main/java/io/github/marioluan/datastructures/priority/queue/MaxBinaryHeap.java:10: Comment matches to-do format 'TODO'. [TodoComment]
[ant:checkstyle] [INFO] /home/gradle/src/main/java/io/github/marioluan/datastructures/symboltable/BinarySearchTree.java:487: Comment matches to-do format 'TODO'. [TodoComment]