moved column and table class from namespace sql to query

source/orm/sql/record.cpp

@@ -1,5 +1,4 @@
 #include "matador/sql/record.hpp"
-#include "matador/sql/column.hpp"
 
 #include <algorithm>
 #include <stdexcept>
@@ -67,9 +66,8 @@ const std::vector<record::field_ref> &record::columns() const
 //  return columns_[pk_index_];
 //}
 
-const field &record::at(const sql::column &col) const
-{
-  const auto &res = fields_by_name_.at(col.column_name());
+const field &record::at(const std::string &name) const {
+  const auto &res = fields_by_name_.at(name);
   const auto &f = res.first;
   return f;
 }