Numeric on-disk index write and search

Includes:
  - The disk/v1/kdtree package containing the
kdtree writer and reader
  - The implementation code to tie these into
the existing read and write paths. The main parts
of this are the NumericIndexWriter and the
NumericIndexSegmentSearcher
  - Additional testing for the new code

patch by Mike Adamson; reviewed by Caleb Rackliffe and Andres de la Peña for CASSANDRA-18067

Co-authored-by: Mike Adamson <madamson@datastax.com>
Co-authored-by: Caleb Rackliffe <calebrackliffe@gmail.com>
Co-authored-by: Piotr Kołaczkowski <pkolaczk@gmail.com>
Co-authored-by: Jason Rutherglen <jason.rutherglen@gmail.com>
Co-authored-by: Zhao Yang <zhaoyangsingapore@gmail.com>
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