Allow for unauthenticated requests

Fixes gh-187

Author: AurelioDeRosa

README.md

@@ -57,9 +57,17 @@ var github = new Github({
 });
 ```
 
-You can use either:
+Some information, such as public Gists, can be accessed without any authentication. For such use cases, you can create
+a Github instance as follows:
+
+```js
+var github = new Github();
+```
+
+In conclusion, you can use:
 * Authorised App Tokens (via client/secret pairs), used for bigger applications, created in web-flows/on the fly
 * Personal Access Tokens (simpler to set up), used on command lines, scripts etc, created in GitHub web UI
+* No authorization
 
 See these pages for more info:
 

dist/github.bundle.min.js

@@ -43,6 +43,8 @@
    // -------------
 
    var Github = function (options) {
+      options = options || {};
+
       var API_URL = options.apiUrl || 'https://api.github.com';
 
       // HTTP Request Abstraction

dist/github.bundle.min.js.map

@@ -23,6 +23,21 @@ describe('Github constructor', function() {
    });
 });
 
+describe('Github constructor without authentication data', function() {
+   it('should read public information', function(done) {
+      var github = new Github();
+      var gist = github.getGist('f1c0f84e53aa6b98ec03');
+
+      gist.read(function(err, res, xhr) {
+         should.not.exist(err);
+         xhr.should.be.instanceof(XMLHttpRequest);
+         res.should.be.an('object');
+
+         done();
+      });
+   });
+});
+
 describe('Github constructor (failing case)', function() {
    before(function() {
       github = new Github({