Use formatters for custom vendored content types.

[tylerdooling]

Summary

When using custom vendored content types the specified formatters were not being used because only the generalized type was being made available to match.

Grape::Middleware::Formatter#mime_array - when provided with accept header application/vnd.mycompany.upcase+txt - has previously returned

[ 'application/txt']

and now returns

['application/vnd.mycompany.upcase+txt',  'application/txt']

This allows Grape::Middleware::Formatter#format_from_header to match the custom type and proceed to use the custom formatter.

Example

class Hello < Grape::API
  content_type :upcase, 'application/vnd.mycompany.upcase+txt'
  formatter :upcase, ->(obj, env){ obj.upcase }
  content_type :dashed, 'application/vnd.mycompany.dashed+txt'
  formatter :dashed, ->(obj, env){ obj.tr(' ', '-') }

  get :test do
    'hello world'
  end
end

# Before
$ curl localhost:9292/test -H 'Accept: application/vnd.mycompany.upcase+txt'
# status 406

$ curl localhost:9292/test -H 'Accept: application/vnd.mycompany.dashed+txt'
# status 406

# After
$ curl localhost:9292/test -H 'Accept: application/vnd.mycompany.upcase+txt'
# Content-Type: application/vnd.mycompany.upcase+txt
# HELLO WORLD

$ curl localhost:9292/test -H 'Accept: application/vnd.mycompany.dashed+txt'
# Content-Type: application/vnd.mycompany.dashed+txt
# hello-world

[dblock]

This is great. Does it need a README update as well (probably)?

[tylerdooling]

Thanks @dblock. I'm happy to add to the readme if you've got something in mind. My initial read of it seemed to describe this custom formatter behavior already in the API Formats section. I initially just tried to use it and found that it didn't work for these prefixed types.

[dblock]

I merged this, thanks.

[tylerdooling]

Sure thing - glad to help.