Modularise output formatting with new gwdatafind.io module
This MR migrates the output formatting logic previous in gwdatafind.__main__ into a new gwdatafind.io module to make it more modular and thus easier to add new output formats (see #7).
This MR migrates the output formatting logic previous in gwdatafind.__main__ into a new gwdatafind.io module to make it more modular and thus easier to add new output formats (see #7).