0.6.0

• Return Err instead of panic'ing when opening a database file with an incompatible file format version
• Many optimizations to the file format, and progress toward stabilizing it
• Fix race between read & write transactions, which could cause reads to return corrupted data
• Better document the different WriteStrategys
• Fix panic when recovering a database that was uncleanly shutdown, which had been created with WriteStrategy::Checksum (which is the default)
• Fix panic when using insert_reserve() in certain cases