feat: Postgres Contains and ContainedBy Operators

- sourced from https://github.com/MathewJoseph31/JSqlParser/tree/add-postgress-nested-WithClause
- resolves PR #361
- remove redundant comments

src/main/java/net/sf/jsqlparser/expression/ExpressionVisitor.java

@@ -43,12 +43,9 @@
 import net.sf.jsqlparser.expression.operators.relational.MinorThan;
 import net.sf.jsqlparser.expression.operators.relational.MinorThanEquals;
 import net.sf.jsqlparser.expression.operators.relational.NotEqualsTo;
-import net.sf.jsqlparser.expression.operators.relational.DoubleAnd;// Added by mathew on 21st Nov
-                                                                   // 2016
-import net.sf.jsqlparser.expression.operators.relational.Contains;// Added by mathew on 21st Nov
-                                                                  // 2016
-import net.sf.jsqlparser.expression.operators.relational.ContainedBy;// Added by mathew on 21st Nov
-                                                                     // 2016
+import net.sf.jsqlparser.expression.operators.relational.DoubleAnd;
+import net.sf.jsqlparser.expression.operators.relational.Contains;
+import net.sf.jsqlparser.expression.operators.relational.ContainedBy;
 import net.sf.jsqlparser.expression.operators.relational.RegExpMatchOperator;
 import net.sf.jsqlparser.expression.operators.relational.SimilarToExpression;
 import net.sf.jsqlparser.schema.Column;
@@ -131,11 +128,11 @@ public interface ExpressionVisitor {
 
     void visit(NotEqualsTo notEqualsTo);
 
-    void visit(DoubleAnd doubleAnd);// Added by mathew on 21st Nov 2016
+    void visit(DoubleAnd doubleAnd);
 
-    void visit(Contains contains);// Added by mathew on 21st Nov 2016
+    void visit(Contains contains);
 
-    void visit(ContainedBy containedBy);// Added by mathew on 21st Nov 2016
+    void visit(ContainedBy containedBy);
 
     void visit(ParenthesedSelect selectBody);