Update guides for new rendering options

* Introduces `:plain`, `:html`, `:body` render option.
* Update guide to use `render :plain` instead of `render :text`.

guides/source/action_controller_overview.md

@@ -1088,7 +1088,7 @@ class ApplicationController < ActionController::Base
   private
 
     def record_not_found
-      render text: "404 Not Found", status: 404
+      render plain: "404 Not Found", status: 404
     end
 end
 ```

guides/source/getting_started.md

@@ -608,7 +608,7 @@ look like, change the `create` action to this:
 
 ```ruby
 def create
-  render text: params[:article].inspect
+  render plain: params[:article].inspect
 end
 ```
 

guides/source/layouts_and_rendering.md

@@ -236,15 +236,34 @@ render inline: "xml.p {'Horrid coding practice!'}", type: :builder
 
 #### Rendering Text
 
-You can send plain text - with no markup at all - back to the browser by using the `:text` option to `render`:
+You can send plain text - with no markup at all - back to the browser by using
+the `:plain` option to `render`:
 
 ```ruby
-render text: "OK"
+render plain: "OK"
 ```
 
-TIP: Rendering pure text is most useful when you're responding to Ajax or web service requests that are expecting something other than proper HTML.
+TIP: Rendering pure text is most useful when you're responding to Ajax or web
+service requests that are expecting something other than proper HTML.
 
-NOTE: By default, if you use the `:text` option, the text is rendered without using the current layout. If you want Rails to put the text into the current layout, you need to add the `layout: true` option.
+NOTE: By default, if you use the `:plain` option, the text is rendered without
+using the current layout. If you want Rails to put the text into the current
+layout, you need to add the `layout: true` option.
+
+#### Rendering HTML
+
+You can send a HTML string back to the browser by using the `:html` option to
+`render`:
+
+```ruby
+render html: "<strong>Not Found</strong>".html_safe
+```
+
+TIP: This is useful when you're rendering a small snippet of HTML code.
+However, you might want to consider moving it to a template file if the markup
+is complex.
+
+NOTE: This option will escape HTML entities if the string is not html safe.
 
 #### Rendering JSON
 
@@ -276,6 +295,19 @@ render js: "alert('Hello Rails');"
 
 This will send the supplied string to the browser with a MIME type of `text/javascript`.
 
+#### Rendering raw body
+
+You can send a raw content back to the browser, without setting any content
+type, by using the `:body` option to `render`:
+
+```ruby
+render body: "raw"
+```
+
+TIP: This option should be used only if you explicitly want the content type to
+be unset. Using `:plain` or `:html` might be more appropriate in most of the
+time.
+
 #### Options for `render`
 
 Calls to the `render` method generally accept four options: