ET_DataExtension_Row extends but does not implement Upserts

[TomAshe]

Describe the bug
The ET_DataExtension_Row extends ET_CUDWithUpsertSupport, but does not implement the put() method, which is needed to actually perform an upsert. It only implements post() (for create) and patch() (for update).

To Reproduce

1. Try POSTing a row. Success. The row is created. POST the same row again. Fail. Duplicate primary key.
2. Try PATCHing a row. Fail. There is no row to update. (PATCH only works for existing rows.

Expected behavior
PUT a row. Success. PUT the row again. Success.

Screenshots
None.

Code snippet
None.

Environment

• SDK Version: 1.4
• PHP version: 7.x

The bug has the severity

• Major: The defect affects major functionality or major data. It has a workaround but is not obvious and is difficult.
  Technically, you could work around this by performing a POST, and if it fails, perform a PATCH. (Or vice versa) This is not a good workaround, to perform two calls, when once could be done instead, with minimal code.

Additional context
Add any other context about the problem here.

[TomAshe]

I've submitted a PR to address this issue.

#164