blkio v0.2.0 release

API changes:
- Blkio::start() returns Result<BlkioStartOutcome> and Queues have a separate lifetime from Blkio instances
- Blkio::get_queue() and Blkio::get_poll_queue() have been removed since Blkio::start() returns the Queues now
- Blkio::state() has been added for querying the Created/Connected/Started state
- Queue is now Send + Sync
- Errno, c_char, iovec, and sigset_t are re-exported