Use HTTP Post when retrieving result

[tijmenbruggeman]

When fetching the result of a compression, users call the method result(). This will do a request to an url like: https://api.tinify.com/output/<randomstring> This will resolve to a file.

Because it is possible to add commands to this request such as and other commands, the result would be a GET request with a body. Although this is possible, it is not recommended.

Therefor we should change the method to a POST. Shouldn't be a breaking change so patched the version.