Single-threaded plumber that can run "start" rules.

Thanks to Caerwyn Jones.

include/plumb.h

@@ -0,0 +1,48 @@
+#pragma	lib	"libplumb.a"
+#pragma	src	"/sys/src/libplumb"
+
+/*
+ * Message format:
+ *	source application\n
+ *	destination port\n
+ *	working directory\n
+ *	type\n
+ *	attributes\n
+ *	nbytes\n
+ *	n bytes of data
+ */
+
+typedef struct Plumbattr Plumbattr;
+typedef struct Plumbmsg Plumbmsg;
+
+struct Plumbmsg
+{
+	char		*src;
+	char		*dst;
+	char		*wdir;
+	char		*type;
+	Plumbattr	*attr;
+	int		ndata;
+	char		*data;
+};
+
+struct Plumbattr
+{
+	char		*name;
+	char		*value;
+	Plumbattr	*next;
+};
+
+int			plumbsend(int, Plumbmsg*);
+Plumbmsg*	plumbrecv(int);
+char*		plumbpack(Plumbmsg*, int*);
+Plumbmsg*	plumbunpack(char*, int);
+Plumbmsg*	plumbunpackpartial(char*, int, int*);
+char*		plumbpackattr(Plumbattr*);
+Plumbattr*	plumbunpackattr(char*);
+Plumbattr*	plumbaddattr(Plumbattr*, Plumbattr*);
+Plumbattr*	plumbdelattr(Plumbattr*, char*);
+void			plumbfree(Plumbmsg*);
+char*		plumblookup(Plumbattr*, char*);
+int			plumbopen(char*, int);
+int			eplumb(int, char*);