Support allOf in components

[Antonboom]

Example:

components:
  schemas:
  Transaction:
      type: object
      properties:
        id:
          type: string
        datetime:
          type: string
          description: datetime in format ISO8601
    AccountingTransaction:
      allOf:     # Combines the BasicErrorModel and the inline model
        - $ref: '#/components/schemas/Transaction'
        - type: object
          properties:
            contractID:
              description: Contract id
              type: string
            inn:
              description: tx number
              type: string
            name:
              description: Partner's name
              type: string

type AccountingTransaction struct {
	Transaction
	ContractID string `json:"contractID"`
	INN        string `json:"inn"`
	Name       string `json:"name"`
}