Creating VersionInfo(3, 2, 1, 1) succeeds, but fails later when comparing
it with another VersionInfo instance (for example, v1 < v2):

```
    def split_key(key):
>       return [convert(c) for c in key.split('.')]
E       AttributeError: 'int' object has no attribute 'split'
```

To allow VersionInfo(10) > VersionInfo('2') == True

Add example from python-semver#135

Co-authored-by: Alexander Grund

Co-authored-by: Alexander Grund

* Move assert line to test_should_be_able_to_use_strings_as_major_minor_patch
* Add additional assert, comparing VersionInfo created
  with strings and with integers

Co-authored-by: Alexander Grund

Co-authored-by: Alexander Grund