* Allow to mark JSON properties & XML nodes as optional (#102)

* Add optional expander definition

* Add hasExpander method for Pattern

* Allow mark JSON properties & xml nodes as optional

* Use intuitive matcher type definition in Xml test stock qty node definition

* Add information about optional Expander to README

* Remove return type declaration

* Catch PHPMatcher Exception when parsing pattern for optional values

* Add getName to PatternExpander interface

* Remove unncessary ExpanderInitializer dependency in TypePattern

* Use constants for expander name instead of method

* Redeclare $expanderDefinitions using constants

* Add static is($name) method to PatternExpander interface

* revert php 7.0 feature

* drop php 5.3, 5.4 support

* Use proper test case base class

* Use proper test case base class

* Fixed has expander method