Converts Open Flash Chart 2 <http://teethgrinder.co.uk/open-flash-chart-2/> chart description files (which are written in JSON format) into PNG images. This tool is designed for automation. It can be run from a CRON job or shell script---even in a headless environment (where a graphical display is absent) as the "ofc2_to_png_headless.sh" shell script demonstrates. To see help and usage information, run the `ruby ofc2_to_png.rb` command.