0.1.0-PRE18

• Removed the internal vector caching and instead using sun.misc.Unsafe to speed up vector serialization and deserialization.
  The result is actually faster queries without caching than it previously had with caching.
  Also able to remove the protobuf dependency which was previously used to serialize vectors.
• Upgraded Elasticsearch version from 7.4.0 to 7.6.2.
  Attempted to use 7.7.1 but the Apache Lucene version used in 7.7.x introduces a performance regression (Details).
  Switching from Java 13 to 14 also yields a slight speedup for intersections on sparse vectors.