Fixes #3 Add possibility to pass construct argument

[extdevelopment]

No description provided.

[shouze]

Thank you @extdevelopment :)

I haven't checked yet but are you sure than config property can't be used to do that? Actual code lacks a bit of documentation & tests about that so I'll go deeper to check that on my side prior to merge this PR.

I guess you will to have to make the same PR against master branch (behat 2).

[extdevelopment]

@shouze thx you that you check my PR.

I'm not sure the original goal with config, not documented, possible to use construct argument,
but not in its the present situation.
https://github.com/rezzza/mock-extension/blob/behat3/src/Adapter/AtoumAdapter.php#L42

call_user_func($this->config, $this->mockGenerator);

It would be necessary to define the structure of the config.

If it cleared the right solution, I'm going to do behat 2 master branch also.