Introduce a proper Debian source package build system

It's not perfect - there is no symbol versioning, and I have had to
make some (perhaps false) assumptions about library ABI stability, but
it does produce something vaguely resembling what would be expected
from a library package found in Debian, and it does so using the
standard Debian source format.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

debian/rules

@@ -0,0 +1,49 @@
+#!/usr/bin/make -f
+
+.PHONY: build
+
+VERSION:=$(shell cat VERSION)
+export VERSION
+
+soname:=$(shell echo $${VERSION%%.*})
+WIRINGPI_SONAME_SUFFIX:=.$(soname)
+export soname
+export WIRINGPI_SONAME_SUFFIX
+
+build:
+	dh $@
+
+override_dh_auto_configure:
+
+override_dh_prep:
+	dh_prep -Xdebian/tmp
+
+dirs:
+	dh_installdirs -A
+	mkdir debian/tmp
+	set -e; for p in `dh_listpackages`; do \
+		(cd debian/$$p; find -type d) | \
+		(cd debian/tmp; xargs mkdir -p) \
+	done
+
+override_dh_clean:
+	dh_clean
+	WIRINGPI_SUDO= bash -xe ./build clean
+
+override_dh_auto_build: dirs
+	V=1 LDCONFIG=: WIRINGPI_SUDO= WIRINGPI_SUID=0 \
+	    DESTDIR=`pwd`/debian/tmp/usr \
+	    PREFIX= WIRINGPI_SUDO= \
+	    bash -xe ./build
+
+override_dh_auto_install:
+	dh_install
+	set -ex; for l in libwiringPi libwiringPiDev; do \
+		ln -sf $$l.so.$${VERSION} \
+			debian/libwiringpi$$soname/usr/lib/$$l.so.$$soname; \
+		ln -sf $$l.so.$${VERSION} \
+			debian/libwiringpi-dev/usr/lib/$$l.so; \
+	done
+
+%:
+	dh $@