Select fields using strings or symbols, array or not

[KevinBongart]

Hi! Thanks for this nice and useful gem.

I ran into a tiny inconvenience:

Article.select("title,body").first
# all good

Article.select(["title", "body"]).first
# error

So I thought people who are used to Ruby's flexibility could benefit from calling this method in various convenient ways:

Article.select("title,body").first
Article.select(["title", "body"]).first
Article.select([:title, :body]).first
Article.select("title", "body").first
Article.select(:title, :body).first

(I personally enjoy the last one since ActiveRecord allows the same style, but to each their own.)

This PR brings a patch and a few tests, and if you think this small feature could be useful, I'm happy to refactor a bit with more explicit names, add a comment about the method params, and update the README.

Thanks!

[chingor13]

Thanks!