travis: Add Travis CI support

Currently builds for Ubuntu 15.10 amd64 with gcc 5 under docker.

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/Makefile b/Makefile
index 733511c..7ffbc01 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-CFLAGS	= $(shell pkg-config --cflags libsystemd) -Wall -O2
+CFLAGS	= $(shell pkg-config --cflags libsystemd) -Wall -O2 -g
 LDLIBS	= $(shell pkg-config --libs libsystemd)
 
 ifdef KERNEL_HEADERS