Update to 4.5.3

Upstream changes:
= 4.5.3 (20170102) =

* Fixed foster parenting when html5lib is the tree builder. Thanks to
  Geoffrey Sneddon for a patch and test.

* Fixed yet another problem that caused the html5lib tree builder to
  create a disconnected parse tree. [bug=1629825]

= 4.5.2 (20170102) =

* Apart from the version number, this release is identical to
  4.5.3. Due to user error, it could not be completely uploaded to
  PyPI. Use 4.5.3 instead.

(wen)