add support for authors (plural)

[lucaong]

Echoe supports multiple authors for a gem, but in RubyGems the syntax is:

authors=array_of_authors

see here: http://docs.rubygems.org/read/chapter/20#authors

while in echoe is:

author=string_or_array

authors (plural) seems to raise an error

[evan]

just a string doesn't work for you?

[lucaong]

Yes, and passing an array works equally well. I just think it would be nice to make it more consistent with RubyGems and support the authors method also in its plural form. By the way echoe rocks, and this would be a little improvement more than a fix.

[evan]

Oh, you just want an accessor? That's fine. Pull request please, including change log update.