Building using Github actions (#131)

Change Travis CICD to GitHub Actions

cicd_scripts/check_references.php

@@ -0,0 +1,30 @@
+<?php
+
+function print_usage()
+{
+   fwrite(STDERR,
+    "USAGE:\n"
+         . " php check_references.php mdfile\n"
+         );         
+}
+
+if ($argc < 2) {
+   fwrite(STDERR, "Invalid arguments:\n");
+   print_usage();
+   exit(1);
+}
+
+$mdfile = $argv[1];
+
+$data = file_get_contents($mdfile);
+
+if(preg_match_all('/\[([^\]]+)\][^(:]/', $data."\n",$m))      
+{
+   $references = $m[1];
+   foreach($references as $r)
+   {
+      if(!preg_match("/\[".preg_quote($r,"/")."\]:(.*)/", $data,$m2)){
+         echo "Missing reference for [$r] !\n";
+      }
+   }   
+}