Non-singleton generator cleanup

Updates which are enabled by no longer depending on the Generator singleton:

- Disable process isolation when running tests.
- Update code sample in README with preferred usage
Use PHP VCR for mocking HTTP requests.

This eliminates the dependency for external services.

Running composer update also updated other dependencies. They are included here as well.
Merge pull request #79 from kasperg/php-vcr-test-fixtures

Use PHP VCR for mocking HTTP requests.
Generate getters/setters also for non nullable members. Fix DateTime namespace
Merge branch 'datetime_format' of github.com:Lafriks/wsdl2phpgenerator into master