1.2.0

• Add Builder::create_file() which does the same thing as create() but
  takes a File instead of a path
• Add stats() to tables which provides informational statistics on the table's storage
• Fix WriteTransaction::stats() to correctly count the storage used by multi-map tables
• Fix panics that could occur when operating on savepoints concurrently from multiple threads
  on the same WriteTransaction
• Implement Send for WriteTransaction
• Change MSRV to 1.66
• Performance optimizations