Add the end () method

The end() method is a convenience over .doc().toString().
It converts the entire XML document to string.

README.md

@@ -20,12 +20,12 @@ As a result, version from v0.1.3 are **not** compatible with previous versions.
 
 ``` js
 var builder = require('xmlbuilder');
-var doc = builder.create('root')
+var xml = builder.create('root')
   .ele('xmlbuilder', {'for': 'node-js'})
     .ele('repo', {'type': 'git'}, 'git://github.com/oozcitak/xmlbuilder-js.git')
-  .doc();
+  .end({ pretty: true});
 
-console.log(doc.toString({ pretty: true }));
+console.log(xml);
 ```
 
 will result in:

src/XMLBuilder.coffee

@@ -97,6 +97,11 @@ class XMLBuilder
     return @rootObject
 
 
+  # Ends the document and converts string
+  end: (options) ->
+    return toString(options)
+
+
   # Converts the XML document to string
   #
   # `options.pretty` pretty prints the result

src/XMLFragment.coffee

@@ -233,6 +233,10 @@ class XMLFragment
     return @root().documentObject
 
 
+  # Ends the document and converts string
+  end: (options) ->
+    return @document().toString(options)
+
   # Gets the previous node
   prev: () ->
     if @isRoot

test/test.coffee

@@ -214,3 +214,7 @@ xml14 = '<?xml version="1.1"?><test14><node>test</node></test14>'
 test14 = xmlbuilder.create('test14', { 'version': '1.1' } ).ele('node').txt('test').doc().toString()
 assert.strictEqual(xml14, test14)
 
+# Test the end() method
+xml15 = '<?xml version="1.1"?><test14><node>test</node></test14>'
+test15 = xmlbuilder.create('test14', { 'version': '1.1' } ).ele('node').txt('test').end()
+assert.strictEqual(xml15, test15)