debian: Add breaks/conflicts for libmenu-cache1-dev to make the upgarde nicer
debian: new package libmenu-cache-bin: binaries should not come with library.

Debian packaging rules require that library package should contain
only library itself. There is also another problem: old library can
use newer binaries safely but new library cannot work correctly with
old menu-cached running. And since first menu-cached started wins,
in case when few libmenu-cache* versions are installed, the first
usage of libmenu-cache will start supplied menu-cached and that will
make start another menu-cached impossible. Therefore binaries should
be in separate package which is common for all of libmenu-cache*.
This commit moves binaries into separate package which is
independent of the library soname.
Removing --libexecdir from configure parameters.

The upstream uses pkglibexecdir instead of libexecdir which is set
by dh_auto_configure already so no extra parameter is required.
Changing libmenu-cache2 into libmenu-cache3 due to ABI change.
Correcting libmenu-cache1-dev to oldlibs/extra.

Debian packaging rules says transitional packages should be in
oldlibs/extra to be found by package maneger.
Enabling hardening.

The hardening was previously disabled. It should be not because
it compiles now just fine.
Changing to new upstream version 0.5.0.