Cache of key-value pairs with persistent storage for C++ 11

 This API provides a cache of key-value pairs with a backing store. It is
 intended for caching arbitrary (possibly large) amounts of data, such as
 might be needed by a web browser cache. The cache supports both
 least-recently-used and time-to-live expiration policies. It scales to
 large numbers (millions) of entries and is very fast. The implementation
 is based on leveldb and typically provides throughput many times larger
 than the I/O bandwidth to disk.
 .
 The cache is robust in the face of crashes and power loss. After a
 re-start, it is guaranteed to be in a consistent state with correct
 data. Some number of updates that were made just prior to a power loss
 or kernel crash can be lost; however, if just the calling process
 crashes, all updates that were made prior to the crash are guaranteed to
 be on disk.