Oxigraph RocksDB bindings

RocksDB bindings for Oxigraph.

By default it builds RocksDB as part of this crate. It is also possible to dynamically link to RocksDB using the disabled by default pkg-config feature. In this case pkg-config will be used to link to RocksDB. Refer to this crate documentation if you want to configure the library lookup.

Based on librocksdb-sys under Apache v2 license.