Fix IncludeFixer to comply with the documentation and make it more robust

                         
|Q            |A        |
|---          |---      |
|Bug Fix?     |yes      |
|New Feature? |n        |
|BC Breaks?   |n        |
|Deprecations?|n        |
|Tests Pass?  |yes      |
|Fixed Tickets|#204 #141|
|License      |MIT      |
|Doc PR       |         |

This replaces PR #204 and uses the new Tokens class.

One minor shortcoming is that `""` is no longer replaced with `''`, but this requires deeper knowledge of the string-value. And is more something for another fixer.