Object#in? also accepts multiple parameters

[tadast]

This is just a suggestion, but since the change is quite simple, I've created a pull request. The idea is to allow passing multiple arguments to Object#in? method, like:

animal = "cat"
animal.in?("dog", "cat", "rat")

currently, you'd have to do something like this:

animal = "cat"
animal.in?(["bat", "cat", "rat"])

which is not very nice. Implementation also preserves current behaviour.
Do you think it would be useful?

[wycats]

This was the implementation in Merb. I like it.

[sikachu]

@wycats I originally propose this varargs version in #258, but I think either @dhh or @tenderlove rejected it.

Does @dhh and @tenderlove feels ok after this get merged in?

[fxn]

@tadast could you please update the AS core extensions guide please? Here http://edgeguides.rubyonrails.org/active_support_core_extensions.html#in

[tadast]

@fxn done https://github.com/lifo/docrails/commit/9cf285599c1e99736f5dd9d01f986c19dcf3d4da

[fxn]

@tadast excellent thanks!