Log Message:
3.8.0 (2017-06-03)

Features added
--------------
* ``ElementTree.write()`` has a new option ``doctype`` that writes out a
  doctype string before the serialisation, in the same way as ``tostring()``.

* GH-220: ``xmlfile`` allows switching output methods at an element level.
  Patch by Burak Arslan.

* LP-1595781, GH-240: added a PyCapsule Python API and C-level API for
  passing externally generated libxml2 documents into lxml.

* GH-244: error log entries have a new property ``path`` with an XPath
  expression (if known, None otherwise) that points to the tree element
  responsible for the error. Patch by Bob Kline.

* The namespace prefix mapping that can be used in ElementPath now injects
  a default namespace when passing a None prefix.

Bugs fixed
----------
* GH-238: Character escapes were not hex-encoded in the ``xmlfile`` serialiser.
  Patch by matejcik.

* GH-229: fix for externally created XML documents.  Patch by Theodore Dubois.

* LP-1665241, GH-228: Form data handling in lxml.html no longer strips the
  option values specified in form attributes but only the text values.
  Patch by Ashish Kulkarni.

* LP-1551797: revert previous fix for XSLT error logging as it breaks
  multi-threaded XSLT processing.

* LP-1673355, GH-233: ``fromstring()`` html5parser failed to parse byte strings.

Other changes
-------------
* The previously undocumented ``docstring`` option in ``ElementTree.write()``
  produces a deprecation warning and will eventually be removed.