removal of unsafe code (from libs) + code refactoring

These changes were made in response to warnings issued
by the Firefox validation tool for add-ons.

removal of unsafe code:
=======================

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1. highlight.js

 - "innerHTML"

   all instances of "innerHTML" occur within the method: "highlightBlock".
   this method is just a helper utility.
   * accepts a DOM Element
   * inspects the css class of both the Element as well as its parent,
     to determine whether the name of the language has been specified
   * extracts text (ie: source code) from inside of the Element
   * filters this text through the work-horse method: "highlight"
     - input:  name of language, string of text [raw source code]
     - output: string of text [html formatted source code]
     - notes:  all work is done using regex.
               the DOM isn't touched; it's straight text manipulation.
   * updates Element.innerHTML

   changes required to bring add-on into compliance with the Firefox validation tool:
   * remove the method "highlightBlock";
     it's unused/unreachable code.

   summary of changes made:
   * stubbed the following methods with empty functions:
     - "highlightBlock"
     - "initHighlighting"
     - "initHighlightingOnLoad"

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2. coffee-script.js

 - "eval()", "Function()"

   require["./browser"] uses several features of the javascript language,
   which Firefox deems to be unsafe for use within its add-ons.

   specifically:
    - eval( untrusted_code )
    - Function( untrusted_code )

   observations:
    - the global variable "CoffeeScript" is assigned to: require["./coffee-script"]
    - require["./browser"] does not appear to be reachable through invokation of this function.
    - require["./browser"] appears to be a helper function:
        * attaches an event listener to window.onload
        * searches the DOM for <script> tags having: type="text/coffeescript"
        * foreach: extracts the content, converts it to javascript, evaluates the javascript

   conclusions:
   - this helper functionality isn't needed by a Firefox add-on;
     require["./browser"] can safely be removed.

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code refactoring:
=================

  - previously, the add-on wrote a <pre><code class="javascript"> block of code to the DOM,
    then (conditionally) called the highlight.js method: "highlightBlock" to add syntax highlighting.

  - this code needed to be written,
    such that the highlighting is performed using the highlight.js method: "highlight",
    and the resulting string of html is added to the DOM in a safe manner.