This commit introduces a C implementation of a `json_table`-like function
that processes a JSON string and transforms it into a tabular data structure.

Key features:
- Parses JSON using the cJSON library.
- Implements a basic JSONPath engine for selecting row data and column data.
  Supports `$.object.child`, `$[index]`, and `$.array[*]`.
- Defines data structures for table, rows, and column definitions.
- Converts JSON values to C types (int, double, string), with JSON nulls
  being converted to 0/0.0 for numeric types and NULL for strings.
- Includes a demonstration program (`main.c`) with various examples.
- Provides a Makefile for building the demonstration program.