Upgrade to CSS4J 2.0.2

CSS4J CHANGES
=============

Version 2.0.2
-------------

 * Core:
- NSAC: add LexicalUnit.shallowClone().
- CSSOM: always resolve font-size percentages, even when no top-block font size 
  is available.
- CSSOM: more complete implementation for has() selector.
- CSSOM: the specificity of BEGINS_ATTRIBUTE, ENDS_ATTRIBUTE and 
  SUBSTRING_ATTRIBUTE was not being computed.
- CSSOM: specificity for SUBSEQUENT_SIBLING (a~b) selectors was not being 
  computed.
- CSSOM: support the ':where()' pseudo-class.
- CSSOM: be consistent with the serialization of other combinator selectors and 
  do not put whitespace around DIRECT_ADJACENT ('+').
- CSSOM: fix commit [b41b1dbb] "do not assume that var() with a color fallback 
  always represents a color" for gradients (regression introduced in 2.0.1).
- CSSOM: allow var() values without fallbacks inside gradients.
- CSSOM: when serializing the 'animation' and 'transition' shorthands, do not 
  serialize values that are equal to the initial value of the 'free' property.
- CSSOM: inside gradients, allow var() which could represent angles, sizes or 
  percentages.
- CSSOM: setting a shorthand through a var() was not working for some cases 
  (bug).
- CSSOM: fix NPE when explicitly inheriting from the document element.
- CSSOM: add a getMinifiedCssText(String) implementation to LexicalValue.
- CSSOM: make LexicalValue.serializeMinifiedSequence() public and use it to 
  minify pending substitution values.
- CSSOM [refactor]: move specificity class to its own file.
- Javadoc: overview: STARHACK example makes more sense now.
- Javadoc: other improvements.
- Fix typo in auxiliary text file.

 * Dom4j module:
- Adapt to selector processing update in core module.
- Maven POM: upgrade dom4j dependency to 2.1.3.