Add more examples of php-eval

* Add an example where there are two statements separated by semicolons.
* Add an example that illustrates the subtle difference of wrapping
  statements with double quotes.
Warn the user if migrate-manifest did not find some (or all) of the migrations
Fix symfony/yaml requirement

Updated to minimum of 2.2 but not 3 and higher.
Merge pull request #795 from Kazanir/master

Fix symfony/yaml requirement
Merge pull request #794 from tstoeckler/migrate-manifest-warning

Warn the user if migrate-manifest did not find some (or all) of the migrations
Merge pull request #786 from juampy72/php-eval-use-single-quotes

Add more examples of php-eval
Fix #789. Runserver fails in D8 due to userSingle change.
Per #801, comment out a Make test until a better host is found, or test gets a Mock.