Add parameter/attribute defaults, enums and annotations for API Blueprint

[Erol]

This will include the default and enum metadata when rendering parameters or attributes.

The following parameter declaration:

parameter :status, 'Status', type: :string, default: 'completed', enum: %w[pending complete]

Would be rendered as:

+ Parameters
  + status (optional, string) - Status
      + Default: `complete`
      + Members
          + `pending`
          + `complete`

I've also added the ability to add raw API Blueprint annotations for object attributes, which is useful when describing JSONAPI payloads:

attribute :data, type: :object, required: true, annotation: <<~MARKDOWN
    + attributes (required, object)
        + name (required, string)
MARKDOWN

This will be rendered to:

+ Attributes (object)
  + data (required, object) - 
      + attributes (required, object)
          + name (required, string)

[Erol]

Do you have some feedback for this @oestrich?

[alebian]

I am having the same problem with minimum and maximum attributes, can we fix that too in this PR?

[Erol]

I'd like to get the heads up from a contributor first if this PR is worth merging. I can open a new one after

[Erol]

Hi @oestrich, can I get a feedback for this PR?

[oestrich]

Hey @Erol it looks good, can you just add a few tests around it? I can merge it after that.

[Erol]

Sure @oestrich, I'll give you the heads up once the tests are done

[Erol]

Hi @oestrich, I've updated the PR with tests

[oestrich]

Thanks!