Added beau-std as an auto-loaded plugin. (#18)

This means that beau-std will automatically be loaded if available in
the same space as Beau. beau-std is a set of commonly used plugins,
these map directly to nodejs features that are commonly needed within
Beau.

src/__mocks__/beau-std.js

@@ -0,0 +1,7 @@
+class BeauStd {
+	constructor(registry, settings) {
+		registry.defineDynamicValue('createReadStream', () => {});
+	}
+}
+
+module.exports = BeauStd;

src/__mocks__/requireg.js

@@ -1,3 +1,15 @@
-module.exports = function(name) {
-    return require(name);
+function requireg(name) {
+	return require(name);
+}
+
+requireg.std_resolving = false;
+
+requireg.resolve = function(name) {
+	if (requireg.std_resolving) {
+		return '';
+	} else {
+		throw new Error(`Failed to resolve.`);
+	}
 };
+
+module.exports = requireg;

src/__tests__/plugins.spec.js

@@ -3,14 +3,16 @@ const Config = require('../config');
 const Plugins = require('../plugins');
 const Request = require('../request');
 const RequestCache = require('../requestCache');
+const requireg = require('requireg');
 
 describe(`Beau's plugin system`, () => {
     let config;
     let request;
     let plugins;
+    let doc;
 
     beforeEach(() => {
-        const doc = yaml.safeLoad(`
+        doc = yaml.safeLoad(`
             version: 1
             endpoint: 'http://example.com'
 
@@ -32,6 +34,13 @@ describe(`Beau's plugin system`, () => {
         expect(plugins.registry.dynamicValues.length).toBe(1);
     });
 
+    it(`should load autoload plugins`, () => {
+        requireg.std_resolving = true;
+        config = new Config(doc);
+        expect(config.PLUGINS.registry.dynamicValues.length).toBe(2);
+        requireg.std_resolving = false;
+    });
+
     it(`should throw if given an invalid configuration`, () => {
         expect(() => new Plugins([{ test1: true, test2: true }])).toThrow();
     });

src/plugins.js

@@ -5,7 +5,7 @@ const { toKebabCase, dynamicValueRegex, replaceInObject } = require('./shared');
 const isPlainObject = require('is-plain-object');
 
 class Plugins {
-    constructor(plugins = []) {
+    constructor(plugins = [], autoload = ['std']) {
         this.registry = {
             preRequestModifiers: [],
             postRequestModifiers: [],
@@ -15,6 +15,12 @@ class Plugins {
         this.context = {};
 
         plugins.forEach(plugin => this.loadPlugin(plugin));
+        autoload.forEach(plugin => {
+            try {
+                requireg.resolve(plugin);
+                this.loadPlugin(plugin);
+            } catch (e) {}
+        });
     }
 
     loadPlugin(plugin) {