Temporary file and folder support for Files (https://github.com/JohnSundell/Files)

Files+temporary.swift

public extension Folder {
     /// Create a new uniquely-named file within this folder.
     /// - Parameter prefix: (optional) prefix to add the temporary file name
     /// - Parameter fileExtension: (optional) file extension (without the `.`) to use for the created file
     /// - Parameter contents: (optional) the data to write to the file
     /// - throws: `WriteError` if a new file couldn't be created.
     func createTemporaryFile(prefix: String? = nil, fileExtension: String? = nil, contents: Data? = nil) throws -> File {
         var tempFilename = ""
         if let prefix = prefix {
             tempFilename += prefix + "_"
         }
         tempFilename += ProcessInfo.processInfo.globallyUniqueString
         if let fileExtension = fileExtension {
             tempFilename += "." + fileExtension
         }
         return try self.createFile(at: tempFilename, contents: contents)
     }

     /// Create a new uniquely-named folder within this folder.
     /// - Parameter prefix: (optional) prefix to add the temporary folder name
     /// - throws: `WriteError` if a new folder couldn't be created.
     func createTemporarySubfolder(prefix: String? = nil) throws -> Folder {
         var tempFolderName = ""
         if let prefix = prefix {
             tempFolderName += prefix + "_"
         }
         tempFolderName += ProcessInfo.processInfo.globallyUniqueString
         return try self.createSubfolder(named: tempFolderName)
     }
 }