Change how we handle Accepts and Content-Type

[paulcsmith]

Right now the param parser correctly parses the Content-Type

lucky/src/lucky/params.cr

Lines 384 to 394 in b5d6056

	private def json?
	content_type.try(&.match(/^application\/json/))
	end
	private def multipart?
	content_type.try(&.match(/^multipart\/form-data/))
	end
	private def content_type : String?
	request.headers["Content-Type"]?
	end

But when check what the request wants in return we incorrectly use Content-Type but we should instead use Accept.

I think we can keep the same html?|json?|etc methods, but they should all use the Accept header instead of Content-Type

Prior art

• https://blog.bigbinary.com/2010/11/23/mime-type-resolution-in-rails.html
• https://til.hashrocket.com/posts/02e3ee8fd1-how-rails-responds-to-
• https://hexdocs.pm/phoenix/1.4.9/Phoenix.Controller.html#accepts/2
• https://github.com/rails/rails/blob/d1ffe59ab5fd6e811833c127d43b32e87b5d7131/actionpack/lib/action_dispatch/http/mime_negotiation.rb
• https://webmasters.stackexchange.com/questions/31212/difference-between-the-accept-and-content-type-http-headers
• List of default Accept values - HTTP | MDN
• https://blog.arkency.com/2016/03/creating-new-content-types-in-rails-4-dot-2/