allow `requires` to be an object

[kraf]

What would you think about requires (and maybe similar options) additionally accepting an object, e.g.

{
  'node': '>= 4.0.0',
  'libpng': ''
}

This would allow me to specify a default set of dependencies for most of my projects, but be able to override the version with a config merge. I can do the implementation, but I first wanted to know your opinion on this.

[paulcoyle]

I think this is a great idea; sometimes it is simpler to assemble a map than to piece together an array.