0.15.0

• Add Database::check_integrity() to explicitly run repair process (it is still always run if needed on db open)
• Change list_tables() to return a TableHandle
• Change delete_table() to take a TableHandle
• Make insert_reserve() API signature type safe
• Change all iterators to return Result and propagate I/O errors
• Replace WriteStrategy with Durability::Paranoid
• Remove Builder::set_initial_size()
• Enable db file shrinking on Windows
• Performance optimizations