Bump debhelper version to 9 (was 8); update debian/compat.
Update debian/control using wrap-and-sort tool.
Delete version requirements for some build dependencies.
Bump Standards-Version to 3.9.5 (was 3.9.4): no changes required.
Update debian/watch:

git tags are available at project github repo now.
Update debian/rules:

- simplify rules after switching to debhelper 9
- add --list-missing option to dh
- update get-orig-source section after changes in upstream
Delete patch add-hardening-flags-in-compiler-options:

fixed in upstream.
Update debian/copyright.
Update debian/changelog.