On the fly indexing support for large files

[newhoggy]

Total memory usage for traversing 29G JSON file is 5.26G

$ ls -lh ~/zmap2.json
-rw-r--r--  1 jky  staff    29G  2 Jul 08:00 /Users/jky/zmap2.json
time hw-json count --input ~/zmap2.json --expression '"ip"'
Running
Created cursor
==> 7387166
hw-json count --input ~/zmap2.json --expression '"ip"'  107.13s user 98.66s system 55% cpu 6:11.02 total