allow APIs to declare additional content-types

[joeyAghion]

Let's support content-types beyond the built-in XML, JSON, Atom, RSS, and text.

class Twitter::API < Grape::API
  content_types :xls => "application/vnd.ms-excel"
end

[dblock]

Should this allow you to overwrite content-types altogether? This could be achieved by adding a content_type method that adds and a content_types method (this one) that overwrites.

[joeyAghion]

I like the notion of refashioning this to content_type (rather than the plural)... makes it more clear that it's additive. See latest commit; updated interface is:

class Twitter::API < Grape::API
  content_type :xls, 'application/vnd.ms-excel'
end

And I understand the content_types idea, but I don't personally need it and it's a break from the handling of other format settings (which are typically merged together), so I suggest leaving that until it's useful for someone.

[dblock]

Nice and clean. Merging.