Major update.

* Add support for ISO Schematron.
* Remove support for Schematron 1.5.
* Remove the customization stylesheet (integrate customizations into
  the main skeleton directly). This avoids the need for another
  intermediate transformation or issues with <xsl:import> when running
  the code from a PHAR archive or using HHVM where the data: scheme
  is not yet supported.
* Add unit tests for schematron rules embedded in RNG/XSD schemae.
* Add line information about failures in reports.
  Note: on versions of libxml before 2.9, the line information may be
  incorrect in very big XML documents (> 65535 lines).
* Add travis-ci configuration.
Add missing license information about the skeleton.