Packtools

* Updates the HTMLGenerator to support the build of the most recent version of
the articles in HTML.

* Initial support for SciELO PS 1.7.
* Adds support to JATS 1.1.
* Removes Python 3.3 and adds lxml 3.8 and 4.0 to the test matrix.

* Fixes a bug that would cause ``etree.XMLParser`` to raise TypeError on
some old versions of lxml.

* Reduces the size of the test matrix so tests run on a reasonable amount of
time (the full matrix was taking almost 1 hour to run). Now we are testing
against minor versions of lxml 3.4, 3.5 and 3.6 , except for 3.7.x
series where we also test patch versions.
* Fixes bug that would cause wheel distributions to handle dependencies
incorrectly.

* Fixes bugs and regressions.

* [Backwards incompatible] Major changes on ``packtools.domain.XMLValidator``
initializer and ``.parse`` classmethod. The param ``extra_schematron`` is
now deprecated. Use ``sch_schemas`` and ``extra_sch_schemas`` instead, since
both params accept an arbitrary number of schematron schemas.
* Validation logic was abstracted and moved to Validator objects
(``packtools.domain.PyValidator``, ``packtools.domain.DTDValidator``, and
``packtools.domain.SchematronValidator``).
* The stylechecker utility exits 0 on success, and >0 if an error occurs
[https://github.com/scieloorg/packtools/issues/118].
* The values in attribute ``country`` are checked against ISO3166 alpha-2
list.
* Fixes a bug that would cause element's text to be printed out on error
messages instead of the element's name
[https://github.com/scieloorg/packtools/issues/123].
* [Backwards incompatible] Major changes to the data structure returned by
``packtools.stylechecker.summarize`` and, as consequence, to the
JSON-encoded data structure produced by the stylechecker command-line tool
[https://github.com/scieloorg/packtools/issues/75].
* The parsing of schematron schemas was accelerated by preventing the
collection of the IDs in an auxiliary hash table
[https://github.com/scieloorg/packtools/issues/109].