distro FEATURE debian packaging

Debian packaging files from libyang2-debian-packaging branch
by Ondřej Surý with minimal changes for apkg.

    apkg build -i

results in installable Debian packages on Debian/Ubuntu systems.
diff --git a/distro/pkg/deb/tests/yanglint b/distro/pkg/deb/tests/yanglint
new file mode 100755
index 0000000..ee3ca0a
--- /dev/null
+++ b/distro/pkg/deb/tests/yanglint
@@ -0,0 +1,9 @@
+#!/bin/sh
+
+set -e
+if test -f /usr/share/doc/libyang-tools/examples/ietf-interfaces.yang.gz; then
+	gunzip -c < /usr/share/doc/libyang-tools/examples/ietf-interfaces.yang.gz > /tmp/ietf-interfaces.yang
+else
+	cp /usr/share/doc/libyang-tools/examples/ietf-interfaces.yang /tmp/ietf-interfaces.yang
+fi
+yanglint /tmp/ietf-interfaces.yang