Render multi checkbox widget.

def scopes_multi_checkbox(field, **kwargs):
    """Render multi checkbox widget."""
    kwargs.setdefault('type', 'checkbox')
    field_id = kwargs.pop('id', field.id)

    html = [u'<div class="row">']

    for value, label, checked in field.iter_choices():
        choice_id = u'%s-%s' % (field_id, value)

        options = dict(
            kwargs,
            name=field.name,
            value=value,
            id=choice_id,
            class_=' ',
        )

        if checked:
            options['checked'] = 'checked'

        html.append(u'<div class="col-md-3">')
        html.append(u'<label for="{0}" class="checkbox-inline">'.format(
            choice_id
        ))
        html.append(u'<input {0} /> '.format(widgets.html_params(**options)))
        html.append(u'{0} <br/><small class="text-muted">{1}</small>'.format(
            value, label.help_text
        ))
        html.append(u'</label></div>')
    html.append(u'</div>')

    return HTMLString(u''.join(html))