Add support for running headless as a cli about gographs HOT 1 OPEN

@btiernay CLI use should be possible. This project basically wraps a bunch of CLI commands.

1. Install goda and dot (sometimes included in a graphviz package):
   

   gographs/README.md

   Lines 36 to 37 in 8acb808

   	go install github.com/loov/[email protected]
   	brew install dot # or equivalent

2. Repo -> DOT file
   

   gographs/pkg/graph/goda.go

   Lines 8 to 13 in 8acb808

   	// This file takes GoLang repos as input and outputs DOT files:
   	//
   	// 1. repo => dir
   	// git clone --depth 1 https://github.com/siggy/gographs /repos/https://github.com/siggy/gographs"
   	// 2. dir => dot
   	// goda graph -short -cluster github.com/siggy/gographs...

3. DOT file -> SVG
   

   gographs/pkg/render/render.go

   Lines 3 to 13 in 8acb808

   	// This package takes GoLang repos as input and outputs SVG and DOT files:
   	//
   	// 1. repo => dot
   	// curl --data '{"repo":"github.com/siggy/gographs","cluster":true}' -X POST [graph-addr]/graph
   	// 2. dot => svg
   	// echo "..." | \
   	// dot -Tsvg \
   	// -Gfontname=Roboto,Arial,sans-serif \
   	// -Nfontname=Roboto,Arial,sans-serif \
   	// -Efontname=Roboto,Arial,sans-serif \
   	// -o graph2.svg

from gographs.