0.6.4

Magnus 0.6.4 is a patch release, with 1 fix.

Lazy could deadlock when called for the first time from multiple threads simultaneously.

The fix for results in a slight change in expected behaviour. If multiple threads attempt first access at the same time the func given to Lazy::new may be called more than once, but all threads will receive the same value.

Thanks to @choubacha for reporting this issue, along with an excellent repro.