B-tree v2.0.0-alpha.0

• Remove async from package name.
• Upgrade destructible to 6.2.1. Closes #567.
• Upgrade prospective to ^0.2.0. Closes #566.
• Upgrade interrupt to ^10.0.3. Closes #565.
• Upgrade proof to ^9.0.2. Closes #564.
• Replace Fracture with Turnstile. Closes #563.
• Fix stashed load, depenent structure. See #20.
• Preserve a log of loads, dependents. See #20.
• Remove unused dependency tracking key formats. See #20.
• Sketch of vacuum. See #20.
• Make branch split, root fill to async/await. Closes #561. Closes #562.
• Add optional entries collection to descend. Closes #560.
• Further tidy of _path and _hold vs _create. See #558. See #559.
• Create separate cache _create helper. Closes #559.
• Use _path helper in Journalist. Closes #558.
• Make the default merge count one. Closes #557.
• Replace _dirty map with Turnstile.Set. Closes #556.
• Fix cache entry leak in page split. Closes #555.
• Fix split branch test. See #550.
• Convert leaf merge to async/await. Closes #553.
• Deserialize deletes. Closes #554.
• Tidy leaf split for leaf merge. See #553.
• Remove pause from split test. See #548.
• Remove dead code.

Closes #568.