v3.0.0

Breaking changes

• Bulk now requires C++20.
• bulk::index now represents indices as size_t

Added

• Add clear_queues argument to world::sync, to optionally retain all messages
  from the previous superstep.
• Expose clear method of queue.
• Add DGEMM example (Cannon's algorithm).

Changed

• Default barrier for thread backend is now std::barrier.
• Added Barrier concept, and constrain the associated environment and
  world parameters.
• Span based coarray puts are now based on std::span.

Removed

• bulk::span was removed in favor of std::span.

Fixed

• Prevent bulk::sum and bulk::product from silently truncating values (@TimoMaarse, #11)
• Fix const correctness of bulk::product(bulk::world&, T).
• Fix data race in shared state creation for world::split in the thread backend.
• Explicitly cast to T* in the implementation of bulk::coarray:data.