Please support header rows in RestructuredText output

>>> from astropy.table import QTable
>>> import astropy.units as u
>>> import sys
>>> tbl = QTable({'wave': [350,950]*u.nm, 'response': [0.7, 1.2]*u.count})
>>> tbl.write(sys.stdout,  format="ascii.rst")
===== ========
 wave response
===== ========
350.0      0.7
950.0      1.2
===== ========
>>> tbl.write(sys.stdout,  format="ascii.fixed_width", header_rows=["name", "unit"])
|  wave | response |
|    nm |       ct |
| 350.0 |      0.7 |
| 950.0 |      1.2 |
>>> tbl.write(sys.stdout,  format="ascii.rst", header_rows=["name", "unit"])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/astropy/table/connect.py", line 129, in __call__
    self.registry.write(instance, *args, **kwargs)
  File "/usr/lib/python3/dist-packages/astropy/io/registry/core.py", line 369, in write
    return writer(data, *args, **kwargs)
  File "/usr/lib/python3/dist-packages/astropy/io/ascii/connect.py", line 26, in io_write
    return write(table, filename, **kwargs)
  File "/usr/lib/python3/dist-packages/astropy/io/ascii/ui.py", line 856, in write
    writer = get_writer(Writer=Writer, fast_writer=fast_writer, **kwargs)
  File "/usr/lib/python3/dist-packages/astropy/io/ascii/ui.py", line 800, in get_writer
    writer = core._get_writer(Writer, fast_writer, **kwargs)
  File "/usr/lib/python3/dist-packages/astropy/io/ascii/core.py", line 1719, in _get_writer
    writer = Writer(**writer_kwargs)
TypeError: RST.__init__() got an unexpected keyword argument 'header_rows'