fragile

• Implement Future and Stream for Fragile, Sticky and SemiSticky. #38, #40
• Better panic error reporting by adding #[track_caller].
• Fragile now internally uses the stdlib's thread IDs instead of its own counter. #39

• Fixed a soundness issue with Sticky if the slab variant was enabled. This caused a use after free if the type was freed in the wrong thread. #37

• Fragile no longer boxes internally.
• Sticky and SemiSticky now require the use of stack tokens. For more information see #26
• Sticky now tries to drop entries from the thread local registry eagerly if it's dropped on the right thread.

• Fixed non slab versions only allowing a single sticky.

Note on safety: the Sticky and SemiSticky types allow data to live longer than the wrapper type which is why they are now requiring a 'static bound. Previously it was possible to create a sticky containing a bare reference which permitted unsafe access.

• Sticky now requires 'static.
• Added the slab feature for an internal optimization for Sticky to use a slab instead of a HashMap.