v4.20.0

• Record StorageManager cache behaviour in internal error reports
  #588

• Delete empty files left in cache directory, preventing an erroneous source of minimal error reports
  #591

• Report internal errors when serialization fails
  #581

• Buffer IO when reading from cached error files, improving SDK performance
  #573

• Prevent internal error reporting of FileNotFoundException during Delivery
  #594

Bug fixes

• flushOnLaunch() does not cancel previous requests if they timeout, leading to potential duplicate reports
  #593

• Alter value collected for device.freeDisk to collect usable space in internal storage,
  rather than total space in internal/external storage
  #589

• Buffer io when reading from cached error file
  #573