DOCS Email docs and upgrade notes

docs/en/02_Developer_Guides/10_Email/index.md

@@ -38,7 +38,7 @@ to `*text*`).
 
 <div class="info" markdown="1">
 The default HTML template for emails is named `GenericEmail` and is located in `framework/templates/SilverStripe/Email/`.
-To customise this template, copy it to the `mysite/templates/Email/` folder or use `setTemplate` when you create the 
+To customise this template, copy it to the `mysite/templates/Email/` folder or use `setHTMLTemplate` when you create the 
 `Email` instance.
 </div>
 
@@ -58,7 +58,7 @@ The PHP Logic..
 
 ```php
 $email = SilverStripe\Control\Email\Email::create()
-    ->setTemplate('Email\\MyCustomEmail') 
+    ->setHTMLTemplate('Email\\MyCustomEmail') 
     ->setData(array(
         'Member' => Member::currentUser(),
         'Link'=> $link,
@@ -79,6 +79,18 @@ As we've added a new template file (`MyCustomEmail`) make sure you clear the Sil
 take affect.
 </div>
 
+#### Custom plain templates
+
+By default SilverStripe will generate a plain text representation of the email from the HTML body. However if you'd like
+to specify your own own plaintext version/template you can use `$email->setPlainTemplate()` to render a custom view of
+the plain email:
+
+```php
+$email = new Email();
+$email->setPlainTemplate('MyPlanTemplate');
+$this->send();
+```
+
 ## Administrator Emails
 
 You can set the default sender address of emails through the `Email.admin_email` [configuration setting](/developer_guides/configuration).

docs/en/04_Changelogs/4.0.0.md

@@ -15,6 +15,7 @@ guide developers in preparing existing 3.x code for compatibility with 4.0
   * [ORM API](#overview-orm)
   * [Filesystem API](#overview-filesystem)
   * [Template and Form API](#overview-template)
+  * [Email and Mailer](#overview-mailer)
 * [Commit History](#commit-history)
 
 ## <a name="overview"></a>Highlights of major changes
@@ -1174,3 +1175,16 @@ handle field-level and form-level messages. This has the following properties:
 * Removed `PermissionCheckboxSetField::getAssignedPermissionCodes()` (never implemented)
 * `Requirements::delete_combined_files()` and `Requirements::delete_combined_files()` methods have been removed
  as they are obsolete.
+
+### <a name="overview-mailer"></a>Email and Mailer
+
+* `Mailer` converted to an interface
+* `SwfitMailer` added as new default mailer
+* `Email` re-written to be powered by [SwiftMailer](https://github.com/swiftmailer/swiftmailer)
+
+
+#### <a name="overview-orm-api"></a>Email Additions / Changes
+
+* Default template body variable renamed from `$Body` to `$EmailContent`
+* `$email->setTemplate()` renamed to `$email->setHTMLTemplate()`
+* Added `$email->setPlainTemplate` for rendering plain versions of email