B-tree v2.0.0-alpha.47

• Upgrade journalist to 0.1.2. Closes #693.
• Rename Journalist to Sheaf. Closes #692.
• Rename journalist.js to sheaf.js. See #692.
• Move commit script to its own module. Closes #545. Closes #691.
• Sketch of Commit.rename. See #691.
• Try to catch an error presenting on Travis CI.
• Add alias tracking to Commit. See #391.
• Move prepare into Commit. See #691.
• Remove old rename. See #691.
• Update Commit's commit to use the new rename. See #691.
• Remove journalist dependency from Commit. See #691.
• Remove Strata specific emplace and stub. See #691.
• Implement _stub using generic commit. See #691.
• Replace vacuum with one based on a generic commit. See #691.
• Make temporary file relative in generic write file. See #691.
• Create a _writeBranch using generic journal. See #691.

Closes #694.