Reinstate validator.js

It turns out that validator.js is used by the jenkins build script to, uh,
validate the docs.

This partially reverts commit affb106014.

api/package.json

@@ -0,0 +1,15 @@
+{
+  "name": "swagger-cli-validator",
+  "version": "0.0.1",
+  "description": "",
+  "main": "validator.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "nopt": "^3.0.2",
+    "swagger-parser": "^3.2.1"
+  }
+}

api/validator.js

@@ -0,0 +1,71 @@
+"use strict";
+var fs = require("fs");
+var nopt = require("nopt");
+var parser = require("swagger-parser");
+var path = require("path");
+
+var opts = nopt({
+    "help": Boolean,
+    "schema": path
+}, {
+    "h": "--help",
+    "s": "--schema"
+});
+
+if (opts.help) {
+    console.log(
+        "Use swagger-parser to validate against Swagger 2.0\n"+
+        "Usage:\n"+
+        "  node validator.js -s <schema_file_or_folder>"
+    );
+    process.exit(0);
+}
+if (!opts.schema) {
+    console.error("No [s]chema specified.");
+    process.exit(1);
+}
+
+
+var errFn = function(err, api) {
+    if (!err) {
+        return;
+    }
+    console.error(err);
+    process.exit(1);
+};
+
+var isDir = fs.lstatSync(opts.schema).isDirectory()
+if (isDir) {
+    console.log("Checking directory %s for .yaml files...", opts.schema);
+    fs.readdir(opts.schema, function(err, files) {
+        if (err) {
+            console.error(err);
+            process.exit(1);
+        }
+        files.forEach(function(f) {
+            var suffix = ".yaml";
+            if (f.indexOf(suffix, f.length - suffix.length) > 0) {
+                parser.validate(path.join(opts.schema, f), function(err, api, metadata) {
+                    if (!err) {
+                        console.log("%s is valid.", f);
+                    }
+                    else {
+                        console.error("%s is not valid.", f);
+                        errFn(err, api, metadata);
+                    }
+                });
+            } 
+        });
+    });
+}
+else{
+    parser.validate(opts.schema, function(err, api) {
+        if (!err) {
+            console.log("%s is valid", opts.schema);
+        }
+        else {
+            errFn(err, api);
+        }
+    });
+};
+