Add support for mail.ru oauth2

[lexer]

Mail.ru is one of largest mail provider and social network in Russia.

[sferik]

Looks good, thanks!

[sferik]

I spoke too soon. It looks like these commits broke the build: http://travis-ci.org/intridea/omniauth/builds/6922

Damn you merge button!!!

@lexer Did you try running bundle exec rake spec before submitting this pull request?

[lexer]

Sorry, I haven't. =\

Test is broken because of my provider has additional parameter "private_key" that is passed as third parameter. This is not "client secret" and used to create signature to access user info.

According to your API I should put mailru privatekey as hash inside options? Am I correct?

[sferik]

Yes, that is correct. Looking forward to a fix shortly. :)

[sferik]

Any updates on this? The build has been broken for many hours now. If I don't receive a patch soon, I'll have to revert the merge.

[lexer]

i've fixed the problem, but i cannot run specs since i fixed it on my friend's laptop with no ruby installed.

I can pull this commit: lexer@266bf18, but you'd better to run specs by yourself before merging it.