[blog] Implement RSS Feeds

- Task: https://www.odoo.com/web?debug#id=9547&view_type=form&model=project.task
- Pad: https://pad.odoo.com/p/r.SIeozbGyEfAhkzKO
I also get this one

```python
Traceback (most recent call last):
  File "/home/richard/odoo/addons/website/models/ir_http.py", line 207, in _handle_exception
    response = super(ir_http, self)._handle_exception(exception)
  File "/home/richard/odoo/openerp/addons/base/ir/ir_http.py", line 104, in _handle_exception
    return request._handle_exception(exception)
  File "/home/richard/odoo/openerp/http.py", line 617, in _handle_exception
    return super(HttpRequest, self)._handle_exception(exception)
  File "/home/richard/odoo/openerp/addons/base/ir/ir_http.py", line 129, in _dispatch
    result = request.dispatch()
  File "/home/richard/odoo/openerp/http.py", line 635, in dispatch
    r = self._call_function(**self.params)
  File "/home/richard/odoo/openerp/http.py", line 294, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/home/richard/odoo/openerp/service/model.py", line 113, in wrapper
    return f(dbname, *args, **kwargs)
  File "/home/richard/odoo/openerp/http.py", line 291, in checked_call
    return self.endpoint(*a, **kw)
  File "/home/richard/odoo/openerp/http.py", line 754, in __call__
    return self.method(*args, **kw)
  File "/home/richard/odoo/openerp/http.py", line 387, in response_wrap
    response = f(*args, **kw)
  File "/home/richard/odoo/addons/website_blog/controllers/main.py", line 158, in blog
    response = self._blog_feed(blog, blog_post_ids, feed_type)
  File "/home/richard/odoo/addons/website_blog/controllers/main.py", line 209, in _blog_feed
    fg.lastBuildDate(blog_write_date.strftime(timezone_format))
  File "/usr/lib/python2.7/site-packages/feedgen/feed.py", line 462, in lastBuildDate
    return self.updated( lastBuildDate )
  File "/usr/lib/python2.7/site-packages/feedgen/feed.py", line 435, in updated
    updated = dateutil.parser.parse(updated)
  File "/usr/lib/python2.7/site-packages/dateutil/parser.py", line 739, in parse
    timestr = timestr.decode()
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 9: ordinal not in range(128)
```