Use standard autoconf's --docdir (#45)

Use standard autoconf's --docdir (#45)

This removes the version from the doc directory name.

* Use standard autoconf's --docdir

* Initialize autoconf's package name and version

They are used as defaults for --docdir

* Pass PACKAGE_TARNAME to Makefile

No idea why it uses this var instead of PACKAGE

* Cleaned up VERSION variables.

* Fixed VERSION_QUOTED.

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Co-authored-by: Thibault Godouet <yo8192@users.noreply.github.com>