Otherwise the date is not valid.

It does not work straight away with compat level v11.

Include /usr/share/dpkg/architecture.mk and .../pkg-info.mk to provide
DEB_HOST_* and SOURCE_DATE_EPOCH, instead of getting them through shell
invocations.

- Stop using priority "extra" for the -doc package

... the one containing the examples to compile and test

- restrict time of files in examples tar file
- use gzip -n

- dh flags --parallel are not needed
- autoreconf is invoked by default