Start of new ANTLR4 based parser.

Very simple tests pass.

pglablib/sqlast/SelectList.cpp

@@ -0,0 +1,18 @@
+#include "SelectList.h"
+#include "SelectItem.h"
+
+using namespace sqlast;
+
+SelectList::SelectList()
+{
+}
+
+void SelectList::Add(std::unique_ptr<SelectItem> select_item)
+{
+    list.push_back(std::move(select_item));
+}
+
+int SelectList::Count() const
+{
+    return static_cast<int>(list.size());
+}