Converted to Maven project

This changes RedBlackNode into a Maven project, by adding pom.xml and changing the directory structure. This should make it easier for other projects to include RedBlackNode as a dependency.

src/test/java/com/github/btrekkie/interval_tree/IntervalTreeNode.java

@@ -0,0 +1,68 @@
+package com.github.btrekkie.interval_tree;
+
+import com.github.btrekkie.red_black_node.RedBlackNode;
+
+/**
+ * A node in an IntervalTree.  See the comments for the implementation of IntervalTree.  Its compareTo method orders
+ * nodes as suggested in the comments for the implementation of IntervalTree.
+ */
+class IntervalTreeNode extends RedBlackNode<IntervalTreeNode> {
+    /** The dummy leaf node. */
+    public static final IntervalTreeNode LEAF = new IntervalTreeNode();
+
+    /** The interval stored in this node. */
+    public IntervalTreeInterval interval;
+
+    /** The maximum ending value of an interval in the subtree rooted at this node. */
+    public double maxEnd;
+
+    public IntervalTreeNode(IntervalTreeInterval interval) {
+        this.interval = interval;
+        maxEnd = interval.end;
+    }
+
+    /** Constructs a new dummy leaf node. */
+    private IntervalTreeNode() {
+        interval = null;
+        maxEnd = Double.NEGATIVE_INFINITY;
+    }
+
+    @Override
+    public boolean augment() {
+        double newMaxEnd = Math.max(interval.end, Math.max(left.maxEnd, right.maxEnd));
+        if (newMaxEnd == maxEnd) {
+            return false;
+        } else {
+            maxEnd = newMaxEnd;
+            return true;
+        }
+    }
+
+    @Override
+    public void assertNodeIsValid() {
+        double expectedMaxEnd;
+        if (isLeaf()) {
+            expectedMaxEnd = Double.NEGATIVE_INFINITY;
+        } else {
+            expectedMaxEnd = Math.max(interval.end, Math.max(left.maxEnd, right.maxEnd));
+        }
+        if (maxEnd != expectedMaxEnd) {
+            throw new RuntimeException("The node's maxEnd does not match that of the children");
+        }
+    }
+
+    @Override
+    public int compareTo(IntervalTreeNode other) {
+        if (interval.start != interval.end) {
+            return Double.compare(interval.start, other.interval.start);
+        } else {
+            return Double.compare(interval.end, other.interval.end);
+        }
+    }
+
+    @Override
+    public void assertSubtreeIsValid() {
+        super.assertSubtreeIsValid();
+        assertOrderIsValid(null);
+    }
+}