Zend\Cache code split

[gabbydgab]

See full issue: zendframework/zend-cache#93

The reason for that is simply a testing and dependency hell.

1. It's not possible to define a required extension in composer.json so all adapters have to manually check if the current environment is matching the requirements
2. Testing against all adapters is a nightmare and takes very long.

• The travis.yml file al already very complex but it still doesn't test all common cases.
• Some extensions are missing or not 100% compatible for PHP-7 which makes things here more complicated.

3. Doesn't test against different (most common) extension versions
   4.Nearly impossible to run tests for ZendServer adapters
4. another reason is that normally you only need 1 or 2 adapters but that's not very important as zend-cache doesn't install so many files per adapter.