[ruby-mode] Private/protected method definition layout in Ruby 2.1

[Bozhidar Batsov]

Ruby 2.1 has made it possible to define private/protected/public methods on a per method basis (because a `def` now returns a symbol instead of nil). It means that now it’s possible to write code like this:

private def map(attribute, to:)

  @rules[attribute] = to

end

We currently don’t support such an indentation scheme, as `def` is always aligned with `end`:

private def map(attribute, to:)

              @rules[attribute] = to

            end

I’m not saying the first alignment is preferable, but it light of recent changes we did to accommodate similar alignment for `if/unless` it seems like a good idea to add a defcustom supporting the first style as well.

vim already added support for it (https://github.com/vim-ruby/vim-ruby/issues/190).

More on the topic can be read here http://www.sitepoint.com/look-ruby-2-1/.

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Cheers,

Bozhidar