This is a bugfix release to address a few reported issues and also a few
issues that were discovered via my own testing.
* Add a helper method which ensures all data is flushed to disk
* Added additional error handling to prevent malformed DHT messages
crashing the library
* Fixed issue when zeroing unused bits for torrents with an exact
multiple of 32 pieces
* Fixed issue where data could be written to the wrong file if a file
with the same name existed in multiple torrents
* Fixed the handling of torrents where the last file(s) are of zero
length
* Fixed regression with global download rate limiting
* Fixed a performance regression with the new piece picking pipeline
which resulted in lots of CPU cycles being used up on peers which
have not sent an unchoke message
