* d3.v3.js, graph.js: New files. * Makefile.am (EXTRA_DIST): List them. * guix/graph.scm (%d3js-backend): New variable. (emit-d3js-prologue, emit-d3js-epilogue, emit-d3js-node, emit-d3js-edge): New procedures. (%graph-backends): Add %d3js-backend.