Put each bit of spec in its own directory

I want to change the URLs for the spec sections on the website from
<version>/<section>.html to <section>/<version>.html, to better reflect how we
do the versioning.

This puts each bit of spec in its own directory, updates the index to point to
the right place, and fixes continuserv to deal with directories as well as
files.

This will probably require fixes to the speculator too, but I'll have to come
back to that.

scripts/continuserv/main.go

@@ -103,7 +103,7 @@ func makeWalker(base string, w *fsnotify.Watcher) filepath.WalkFunc {
 
 		// log.Printf("Adding watch on %s", path)
 		if err := w.Add(path); err != nil {
-			log.Fatalf("Failed to add watch: %v", err)
+			log.Fatalf("Failed to add watch on %s: %v", path, err)
 		}
 		return nil
 	}
@@ -166,19 +166,34 @@ func populateOnce(dir string) {
 		toServe.Store(bytesOrErr{nil, fmt.Errorf("error generating spec: %v\nOutput from gendoc:\n%v", err, b.String())})
 		return
 	}
-	fis, err := ioutil.ReadDir(path.Join(dir, "scripts", "gen"))
-	if err != nil {
-		toServe.Store(bytesOrErr{nil, err})
-		return
-	}
+
 	files := make(map[string][]byte)
-	for _, fi := range fis {
-		bytes, err := ioutil.ReadFile(path.Join(dir, "scripts", "gen", fi.Name()))
+	base := path.Join(dir, "scripts", "gen")
+	walker := func(path string, info os.FileInfo, err error) error {
 		if err != nil {
-			toServe.Store(bytesOrErr{nil, fmt.Errorf("error reading spec: %v", err)})
-			return
+			return err
 		}
-		files[fi.Name()] = bytes
+		if info.IsDir() {
+			return nil
+		}
+
+		rel, err := filepath.Rel(base, path)
+		if err != nil {
+			return fmt.Errorf("Failed to get relative path of %s: %v", path, err)
+		}
+
+		bytes, err := ioutil.ReadFile(path)
+		if err != nil {
+			return err
+		}
+		files[rel] = bytes
+		return nil
+	}
+
+	err = filepath.Walk(base, walker)
+	if err != nil {
+		toServe.Store(bytesOrErr{nil, fmt.Errorf("error reading spec: %v", err)})
+		return
 	}
 	toServe.Store(bytesOrErr{files, nil})
 }