Add accessors for some parser elements

src/main/java/kroppeb/stareval/element/token/NumberToken.java

@@ -9,6 +9,10 @@ public NumberToken(String number) {
 		this.number = number;
 	}
 
+	public String getNumber() {
+		return number;
+	}
+
 	@Override
 	public String toString() {
 		return "Number{" + this.number + "}";

src/main/java/kroppeb/stareval/element/tree/AccessExpressionElement.java

@@ -11,6 +11,14 @@ public AccessExpressionElement(AccessibleExpressionElement base, String index) {
 		this.index = index;
 	}
 
+	public AccessibleExpressionElement getBase() {
+		return this.base;
+	}
+
+	public String getIndex() {
+		return this.index;
+	}
+
 	@Override
 	public String toString() {
 		return "Access{" + this.base + "[" + this.index + "]}";

src/main/java/kroppeb/stareval/element/tree/BinaryExpressionElement.java

@@ -5,15 +5,27 @@
 
 public class BinaryExpressionElement implements ExpressionElement {
 	private final BinaryOp op;
-	private ExpressionElement left;
-	private ExpressionElement right;
+	private final ExpressionElement left;
+	private final ExpressionElement right;
 
 	public BinaryExpressionElement(BinaryOp op, ExpressionElement left, ExpressionElement right) {
 		this.op = op;
 		this.left = left;
 		this.right = right;
 	}
 
+	public BinaryOp getOp() {
+		return this.op;
+	}
+
+	public ExpressionElement getLeft() {
+		return this.left;
+	}
+
+	public ExpressionElement getRight() {
+		return this.right;
+	}
+
 	@Override
 	public String toString() {
 		return "BinaryExpr{ {" + this.left + "} " + this.op + " {" + this.right + "} }";