Support file types

[raveclassic]

OpenAPI 3.0:

• Requests:
  • single file uploads
  • upload as part of a multipart request
  • file array in a multipart request
• Responses:
  • single application/octet-stream or text/plain file - done in Support binary and text responses #129
  • other types such as application/pdf or text/xml
  • embedded files (type: string + format: byte)