Support struct comments from schema description

[Antonboom]

Example:

components:
  schemas:
  Transaction:
      type: object
      properties:
        id:
          type: string
          description: uuid usually
        datetime:
          type: string
          description: datetime in format ISO8601

type Transaction struct {
        // ID is uuid usually
	ID string `json:"id"`

        // Datetime is datetime in format ISO8601
 	Datetime `json:"id"`
}