RelIdArray uses Enc128 and ByteBuffers... just for the heck of it
added signed encoder and used it in LinkBlock for deltas
added getNodeIdForRelId method to LinkBlock
renamed classes, added interface and docs
added CompressedIdBuffer which uses an encoder and also does run-length-encoding
changed LinkBlock to sue two CompressedIdBuffers, one for the rel-deltas and one for the RelId-NodeId deltas
cleanup
fixed tests to not require bigger heaps
forgot to move one test into the new package