v0.6.4

New

1. fatal! — logs a message at ERROR level, flushes all queued logs, then exits the process with code 1.
2. logger::flush() — waits until every log entry queued before the call has been written out.
3. logger::FatalExt — unwrap_fatal() and expect_fatal() for Result<T, E> (E: Display), which log the error and exit with code 1 on Err.

Full Changelog: v0.6.3...v0.6.4