code: public static ConnectionSource join(final Connection connection) {
          return new ConnectionSource() {
              @Override
              public Connection getConnection() throws SQLException {
                  return new NestedConnection(connection);
              }
          };
      }
docs: A ConnectionSource that will wrap externally managed connection
  with proxy that will omit {@link Connection#close()} or {@link Connection#commit()} calls.
  This is useful to make {@link org.sql2o.Connection} work with externally managed transactions
  @param connection connection to wrap
  @return a connection wrapper that represent a nested connection