InstantiatedIndex - faster but memory consuming index

Represented as a coupled graph of class instances, this all-in-memory index store implementation delivers search results up to a 100 times faster than the file-centric RAMDirectory at the cost of greater RAM consumption.

Performance seems to be a little bit better than log2n (binary search). No real data on that, just my eyes.

Populated with a single document InstantiatedIndex is almost, but not quite, as fast as MemoryIndex.

At 20,000 document 10-50 characters long InstantiatedIndex outperforms RAMDirectory some 30x,
15x at 100 documents of 2000 charachters length,
and is linear to RAMDirectory at 10,000 documents of 2000 characters length.

Mileage may vary depending on term saturation.