Revert "Use releases on upstream's github page, rather than tags"

This reverts commit ec1f3c4571d4934741a6dbffc59abbe7853cdb27.
Do not build-depend on devscripts (>= 2.13.5~)

It is not needed to build twig, but to generate a proper dfsg source
tarball (using uscan). To make source we do not have Twig's documentation
in the source tarball a custom check is added in debian/rules.