Merge pull request #501 from Robalni/master

Header bug and working link
Merge pull request #502 from Robalni/master

Remove duplicates
Removed a dutch book

The book about Latex was in Dutch and not in German.
Merge pull request #503 from TheHippo/patch-1

Removed a dutch book
Update free-programming-books.md

Python in Hydrology has been added to the list.
Merge pull request #504 from ugurthemaster/patch-1

Update free-programming-books.md
Fix Git header
Fix Knockout.js section link