Fixed handling of broken links. Closes #13

- Broken links will be displayed in red background color
- They do no longer abort the display of the directory contents
- A new mime type has been introduced called "link". See the changes
  in en_mimes.php for support in other languages.

Changes:
- Reformatting fun_list.php
- Broken links does no longer lead to display errors.
- fun_list.php: removed dead code, reformatting
- Formatting get_mime_type().
- Links are displayed correctly as links.
- Broken links are displayed in red.