Added Zend\Stdlib\StringUtils::hasPcreUnicodeSupport()
Merge branch 'feature/StringUtils_hasPcreUnicodeSupport' of git://github.com/marc-mabe/zf2 into feature/3495
[#3495] Use StringUtils::hasPcreUnicodeSupport

- Updated Filter classes to use StringUtils::hasPcreUnicodeSupport
- AbstractFilter::hasPcreUnicodeSupport now proxies to
  StringUtils::hasPcreUnicodeSupport
  - docblock marks the method as deprecated
- Added zendframework/zend-stdlib to composer.json (should have been
  there regardless)
Merge branch 'feature/3495' into develop

Close #3495