Improve interpretation of attributes

[NikolayRys]

Status quo

All the params from each widget are being appended to the URL that is being used by the button for the sharing call:
https://github.com/NikolayRys/Likely/blob/master/source/button.js#L216
As I understand, this has been done to unify the way the URL build between all the services.

The problem

This approach doesn't make much sense. Each service constructs the URL in each own way, knows a finite list of parameters, or doesn't use different parameters at all.

1. This leads to the creation of nonsensical URLs.
2. It prevents using custom parameters as to "disable counter" or "default message" for each of the services since they will mess with URL creation.
3. It makes adding new services more difficult.

Proposed solution

Initial change for 2.5:

Add a concept of "known params" for each service. For example, "data-via", but not "data-hello" to Twitter. Continue attaching all the parameters to the URL, but throw console warning each time the parameter not recognised.

Breaking change for 3.0:

Remove the shared logic of constructing URL out of all provided parameters. Instead, do a custom thing in each service according to its capabilities.
Expand the list of known params. Introduce the difference between obligatory params and known, but not obligatory.
Remove warning.

[NikolayRys]

@vitkarpov Could you please share your opinion on this? I'm afraid that somebody might be using this to achieve something.
Like so:
<div class="twitter" data-hello="goodbye">Tweet</div>
that changes URL to:
https://twitter.com/intent/tweet?url={url}&text={title}&hello=goodbye

[vitkarpov]

It all makes sense to me. Let's implement warnings in 2.5 and see who's going to come 😄(probably nobody but that's okay).

[NikolayRys]

Have been fixed in PRs above