distro FEATURE apkg-powered upstream rpm packaging

Using this .spec file originally provided by Martin Winter with some
modifications and apkg magic, I'm able to build both source package

    libyang2-2.0.0.9.gf60c0dbf-1.fc34.src.rpm

and native RPM packages

    libyang2-2.0.0.9.gf60c0dbf-1.fc34.x86_64.rpm
    libyang2-devel-2.0.0.9.gf60c0dbf-1.fc34.x86_64.rpm
    libyang2-tools-2.0.0.9.gf60c0dbf-1.fc34.x86_64.rpm
    libyang2-debuginfo-2.0.0.9.gf60c0dbf-1.fc34.x86_64.rpm
    libyang2-debugsource-2.0.0.9.gf60c0dbf-1.fc34.x86_64.rpm
    libyang2-tools-debuginfo-2.0.0.9.gf60c0dbf-1.fc34.x86_64.rpm

by running

    apkg build -i

on this commit. It should work on any RPM-based distro including SUSE.

I was able to install resulting packages on each testing system.

I've tested this on:

* Fedora 33 VM
* Fedora 34 docker container (fedora:34)
* openSUSE 15 docker container (opensuse/leap)

distro/README.md contains (3 lines of) instructions on howto test this
using apkg in a VM/container/machine of your choice.
diff --git a/tools/make-dev-archive.sh b/tools/make-dev-archive.sh
new file mode 100755
index 0000000..ec3f7ae
--- /dev/null
+++ b/tools/make-dev-archive.sh
@@ -0,0 +1,15 @@
+#!/bin/bash
+# create archive from current source using git
+
+VERSION=$(git describe --tags --always)
+# skip "v" from start of version number (if it exists) and replace - with .
+VERSION=${VERSION#v}
+VERSION=${VERSION//[-]/.}
+
+NAMEVER=libyang-$VERSION
+ARCHIVE=$NAMEVER.tar.gz
+
+git archive --format tgz --output $ARCHIVE --prefix $NAMEVER/ HEAD
+
+# apkg expects stdout to list archive files
+echo $ARCHIVE