Cell area stats and counts tables for the website and C lib

[ajfriend]

Notebooks showing the work for changes in https://github.com/uber/h3/pull/529

Rendered notebooks:

• https://github.com/uber/h3-py-notebooks/blob/cell_stats_1/notebooks/stats_tables/avg_area_table.ipynb
• https://github.com/uber/h3-py-notebooks/blob/cell_stats_1/notebooks/stats_tables/cell_counts.ipynb
• https://github.com/uber/h3-py-notebooks/blob/cell_stats_1/notebooks/stats_tables/extreme_hex_area.ipynb