v2.1.0

The most significant new capability in this release is support for Deno. Deno functionality still has a number of limitations (no async transactions), but core functionality is now available. This release also includes new functionality for supporting asynchronous prefetching for gets, in situations where page faults/disk-I/O are likely. Also includes bug fixes for closing databases. Of particular note is that the close() method is now asynchronous (returns a promise).