Use base image, add Makefile, compress RUN statements to save on disk space

Signed-off-by: Steeve Morin <steeve.morin@gmail.com>

Makefile

@@ -0,0 +1,15 @@
+PLATFORMS = base \
+			android-arm \
+			darwin-x64 \
+			linux-x86 \
+			linux-x64 \
+			linux-arm \
+			windows-x86 \
+			windows-x64
+DOCKER = docker
+IMAGE = steeve/cross-compiler
+
+all:
+	for i in $(PLATFORMS); do \
+		$(DOCKER) build -t $(IMAGE):$$i $$i ; \
+	done