In OpenAPI v3.1 the nullable property was replaced with a "typed array",
that is an array that can either be of type T or null.

To make the minimal amount of changes this commit converts a type array
back into what a 3.0 parser would expect.

Closes #991

@summary now appears before @description. Also don't show "No
description" when the description is not set, instead don't print
anything.

An example:

    /**
     * @description Old description
     *
     * @name oldMethod
     * @summary Short summary
     * @request GET:/api/some/path/old
     */
    oldMethod: (params: RequestParams = {}) =>

    /**
     * @summary Short summary
     * @description New description
     *
     * @name newMethod
     * @request GET:/api/some/path/new
     */
    newMethod: (params: RequestParams = {}) =>