help: add completions

Add :help completion arguments (config, imap, etc). The option "aerc"
brings up the general manpage

Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>
Acked-by: Koni Marti <koni.marti@gmail.com>

commands/help.go

@@ -8,6 +8,19 @@ import (
 
 type Help struct{}
 
+var pages = []string{
+	"aerc",
+	"config",
+	"imap",
+	"notmuch",
+	"search",
+	"sendmail",
+	"smtp",
+	"stylesets",
+	"templates",
+	"tutorial",
+}
+
 func init() {
 	register(Help{})
 }
@@ -17,12 +30,12 @@ func (Help) Aliases() []string {
 }
 
 func (Help) Complete(aerc *widgets.Aerc, args []string) []string {
-	return nil
+	return CompletionFromList(aerc, pages, args)
 }
 
 func (Help) Execute(aerc *widgets.Aerc, args []string) error {
 	page := "aerc"
-	if len(args) == 2 {
+	if len(args) == 2 && args[1] != "aerc" {
 		page = "aerc-" + args[1]
 	} else if len(args) > 2 {
 		return errors.New("Usage: help [topic]")