Add Makefile to build the firmware

We need an automated way to build our firmware. For example, it isn't
clear from this repository which version of gluon we're using.

.gitignore

@@ -0,0 +1 @@
+gluon-build

Makefile

@@ -0,0 +1,25 @@
+GLUON_BUILD_DIR := gluon-build
+GLUON_GIT_URL := git://github.com/freifunk-gluon/gluon.git
+GLUON_GIT_REF := v2014.3.1
+
+JOBS ?= $(shell cat /proc/cpuinfo | grep processor | wc -l)
+
+_GIT_DESCRIBE = $(shell git describe --tags 2>&1)
+ifneq (,${_GIT_DESCRIBE})
+  GLUON_RELEASE := ${_GIT_DESCRIBE}
+endif
+
+all: build
+
+build: gluon-prepare
+	(cd ${GLUON_BUILD_DIR} && make update && make -j ${JOBS})
+
+${GLUON_BUILD_DIR}:
+	git clone ${GLUON_GIT_URL} ${GLUON_BUILD_DIR}
+
+gluon-prepare: ${GLUON_BUILD_DIR}
+	(cd ${GLUON_BUILD_DIR} && git checkout -q ${GLUON_GIT_REF})
+	ln -sfT .. ${GLUON_BUILD_DIR}/site
+
+clean:
+	rm -rf ${GLUON_BUILD_DIR}