SelectField <optgroup> support

[azmeuk]

It would be nice to support optgroup with SelectField and SelectMultipleField. Here is an implementation suggestion:

>>> import wtforms
>>> class F(wtforms.Form):
...     foo = SelectField(choices={
...         "hello": [
...             ("a", "foo"),
...             ("b", "bar"),
...         ],
...         "world": [
...             ("c", "foobaz"),
...             ("d", "barbaz"),
...         ],
...     })
...
>>> F().foo()
<select id="foo" name="foo">
<optgroup label="hello">
<select value="a">foo</select>
<select value="b">bar</select>
</optgroup>
<optgroup label="world">
<select value="c">foobaz</select>
<select value="d">barbaz</select>
</optgroup>
</select>

[jefke-glider]

I suppose it is not possible to have a mixed SelectField, I mean some items with and other without an optgroup?