Include libi3.h (Thanks fernandotcl)

include/libi3.h

@@ -0,0 +1,17 @@
+/*
+ * vim:ts=4:sw=4:expandtab
+ */
+
+#ifndef _LIBI3_H
+#define _LIBI3_H
+
+/**
+ * Try to get the socket path from X11 and return NULL if it doesn’t work.
+ *
+ * The memory for the socket path is dynamically allocated and has to be
+ * free()d by the caller.
+ *
+ */
+char *socket_path_from_x11();
+
+#endif