Dropped twig documentation due to licensing issues

Sadly it is unclear under which license the twig documentaion stands. To no
longer delay twig in Debian, the documentation (for now) has been dropped
out. This results in:
- No longer building binary package twig-doc
- A +dfsg added in the version
- Repacked upstream's source to not include the documentation at all

For further information please reefer to:
https://github.com/fabpot/Twig/issues/1118