docs: def introspect_table(table):
      """Given a SQLAlchemy Table object, return a Shelf description suitable
      for passing to Shelf.from_config.
      """
      d = {}
      for c in table.columns:
          if isinstance(c.type, String):
              d[c.name] = {'kind': 'Dimension', 'field': c.name}
          if isinstance(c.type, (Integer, Float)):
              d[c.name] = {'kind': 'Metric', 'field': c.name}
      return d