Log Message:
py-MechanicalSoup: updated to 0.12.0

Version 0.12

Main changes:
* Changes in official python version support: added 3.7 and dropped 3.4.
* Added ability to submit a form without updating ``StatefulBrowser`` internal
  state: ``submit_selected(..., update_state=False)``. This means you get a
  response from the form submission, but your browser stays on the same page.
  Useful for handling forms that result in a file download or open a new tab.

Bug fixes
* Improve handling of form enctype to behave like a real browser.
* HTML ``type`` attributes are no longer required to be lowercase.
* Form controls with the ``disabled`` attribute will no longer be submitted
  to improve compliance with the HTML standard. If you were relying on this
  bug to submit disabled elements, you can still achieve this by deleting the
  ``disabled`` attribute from the element in the :class:`~mechanicalsoup.Form`
  object directly.
* When a form containing a file input field is submitted without choosing a
  file, an empty filename & content will be sent just like in a real browser.
* ``<option>`` tags without a ``value`` attribute will now use their text as
  the value.
* The optional ``url_regex`` argument to ``follow_link`` and ``download_link``
  was fixed so that it is no longer ignored.
* Allow duplicate submit elements instead of raising a LinkNotFoundError.