Style: Extract is redundant

[Aloento]

According to the results of yesterday's discussion, we will merge the Extract operation into the main method call.

[outcatcher]

Contribution guide should be update accordingly in #390

[Aloento]

@outcatcher This is not all documentation-related issues; this issue also includes longer-cycle refactoring tasks.

[outcatcher]

But it also includes documentation. In most cases labels are used (at least, were used) in "including smth" way. As it includes documentation changes too, in can be marked with that label 🙂

[outcatcher]

Extract methods should be replaced: ExtractIntoSlicePtr and ExtractIntoStructPtr should be make functions.
I would suggest to do that before merging of #381 #384. Other way you have to use workarounds.

[Aloento]

@outcatcher
This is not realistic at the moment, as the methods related to ExtractInto are all under the Result structure.
My idea is to do the first round of refactoring and remove Extract. After that, we will do a second round of refactoring to remove the Result structure completely.

If we want to do this task in one go, then we have to do another independent branch. This will seriously delay the release.
Using progressive, it is also possible to make simultaneous changes to the TF Provider at the same time.