Deprecate `extend` method on a component

[Igorbek]

Reported by @Bdthomson in #33

I am running into the exact same issue with Backbone views such as this one:

MyView.extend({
...
})

produces

TypeError: MyView.extend.withConfig is not a function

Edit:
.extend was removed from styled-components in v4 (styled-components/styled- components#1908), is it possible to remove support for it in this plugin as well so you no longer have to maintain that transformation?

Put up a preliminary PR here - #47.

Suggested solution:

• make extend identifier configurable like other identifiers;
• set default value to an empty array;
• add readme/release notes with breaking change information and instructions to re-enable by providing settings.

[renatonouman]

Hey @Igorbek , it seems like the PR #47 is stale now.
Mind if I pick up this issue and try to come up with a fix?

I saw your comment here and can work towards that.

[Igorbek]

I definitely don't mind, please go ahead @renatonouman if you want.

[renatonouman]

Thanks @Igorbek . I'll give it a go in the next couple of weeks.

[renatonouman]

@Igorbek I created a PR here #370
Let me know if you need anything else and how to move forward.

[Igorbek]

Closed in #370