Issue#21 highlight tokens

Closes #21 

Features Implemented : 

* Automatically highlights C tokens in the editor that correspond to the Linux Man Pages (only from Section 2 and Section 3).
* Opens the corresponding Manual in a new after a highlighted token is clicked or Ctrl-I (Command-I for Mac) is pressed when the cursor is on the highlighted token.
The `Editor` object (which abstracts the ace editor) [has](https://github.com/cs-education/sysbuild/blob/master/app/scripts/editor.js#L179) an `addKeyboardCommand()` function. As mentioned in a comment above, I suggest renaming the `editor` variable to `aceEditor` so that there is no confusion. Then call `editor.addKeyboardCommand()` instead of `aceEditor.commands.addCommand()`.