Defines a file saved in parts using the method upload.saveFilePart.
|id||long||Random file identifier created by the client|
|parts||int||Number of parts saved|
|name||string||Full name of the file|
|md5_checksum||string||In case the file's md5-hash was passed, contents of the file will be checked prior to use|
Saves a part of file for further sending to one of the methods.