Fix for potential XXE/XEE attacks on XML
Use external ZendXml\Security
Use ~ operator with zendxml dep
Autoregister ZendXml namespace/path

- In release builds, ZendXml will ship alongside the Zend library.
Merge branch 'security/zf2014-01'

Resolves ZF2014-01 - XXE/XEE vulnerabilities
[2.2.6] Release readiness

- Created changelog
- Updated README
- Updated `Zend\Version\Version::VERSION`
Merge branch 'security/zf2014-01'

Resolves ZF2014-01 - XXE/XEE vulnerabilities
Merge branch 'releases/2.2.6'

Zend Framework 2.2.6