text: Title: Leading and internal spaces should be preserved in documentation
  Body: Hi,
  I found that `.. code::robotframework` directives cannot work well in resource file format when I set documen format as reStructuredText format.
  
  ```robot
  *** Keywords ***
  Simple keyword
      [Documentation]    
      ...    .. code:: robotframework
      ...
      ...        *** Test Cases ***
      ...        Simple test case
      ...            Simple keyword
  ```
  
  docutils ouput ` <string>:1: (ERROR/3) Content block expected for the "code" directive; none found.` error message.
  
  I had tried to find out why it happen and found that libdoc visit each token and lost white space token. 
  After parse_resource_file function invoked, the doc of keyword remain like the following.
  This is not a valid format for docutils.
  
  ```
  .. code:: robotframework
  
  *** Test Cases ***
  Simple test case
  Simple keyword
  ```
  
  May it possible to reserve white space when using reStructuredText as document format?