phantomjs based exporter for c3 charting library

a configurable command line script based on phantom.js that can export charts to files (server-side of course). Supports `.png`, `.gif`, `.jpeg` and `.pdf` formats, with a config file that allows for extra js (for c3 extentions and over-rides) and extra css. Basic usage:

    path/to/phantomjs outpufile.png options [WxH]

- output can be any path with any of the above supported formats
- c3options is a JSON string to be used in `c3.generate( options )`

The config file also includes a `template` which can be over-ridden. I will later work on an example page showing the usage