integr 1.0.0

This is the first release.

• Added a NEWS.md file to track changes to the package.
• Added a README.md
• The following functionalities are implemented:
  • interactionGraphs() generates an interaction graph object
  • plotIntGraph() plots an interaction graph object (in RStudio)
  • igToGrViz() exports an interaction graph object to a Graphviz file
  • igToSVG() exports an interaction graph object to a SVG image
  • igToPNG() exports an interaction graph object to a PNG image
  • igToPDF() exports an interaction graph object to a PDF file
  • igToPS() exports an interaction graph object to a PS (PostScript) file