arrow

ARROW-372: json vector serialization format

This format serializes the vectors in JSON.
It is not a generic JSON to arrow converter but rather a human readable version of the vectors to help with tests.

Author: Julien Le Dem <julien@dremio.com>

Closes #201 from julienledem/json_file and squashes the following commits:

2e63bec [Julien Le Dem] add missing license
5588729 [Julien Le Dem] refactor tests, improve format
5ef5356 [Julien Le Dem] improve format to allow empty column name
746430c [Julien Le Dem] ARROW-372: Create JSON arrow file format for integration tests