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.
I think using a setter function will be better, as the `editor` can do something when a new `TokenHighlighter` is set.