Increases Line Protocol message length field from 6 to 8 digits
download_inventory performance optimization

LineProtocol changes: previously "attachments" (large data chunks) were sent
only from parent to child, now implemented child to parent.

ParentWorker wait_worker() and process_task() now return list (response, attachment)

Just in case bytes::length() used instead of length()

download_inventory now returned as attachment

Journal is not opened for write if download-inventory does not return data
More adjustments to IPC binary protocol

According to documentation syswrite() should not be used to  send UTF-8 strings to binary files (binmode(), not utf-8 layer). So implementing the following changes:
1) only byte strings are sent now over pipes.
2) only ASCII-7bit encoded strings sent
3) binary data (attachements) can contains any bytes (0-255), but should not have UTF-8 bit set
Version 0.951beta released