Strata v2.0.0-alpha.79

• Upgrade writeahead to 0.0.11.
• Upgrade turnstile to 6.0.0-alpha.50.
• Upgrade destructible to 7.0.0-alpha.38.
• Upgrade turnstile to 6.0.0-alpha.50.
• Upgrade fracture to 0.3.0-alpha.31.
• Open storage in advance of creating Strata.
• No more instances directory when write-ahead only.
• Replace key constant with member variable.
• Rename write-ahead read helpers.

Closes #748.