add sync command to synchronize yanked/deleted files with server

Mentioned in #13 and #36.

comp.go

@@ -37,6 +37,7 @@ var (
 		"delete",
 		"put",
 		"renew",
+		"sync",
 		"echo",
 		"cd",
 		"push",

doc.go

@@ -38,6 +38,7 @@ The following commands are provided by lf with default keybindings.
 
 The following commands are provided by lf without default keybindings.
 
+    sync  synchronizes yanked/deleted files with server
     echo  prints its arguments to the message line
     cd    changes working directory to its argument
     push  simulate key pushes given in its argument

docstring.go

@@ -42,6 +42,7 @@ The following commands are provided by lf with default keybindings.
 
 The following commands are provided by lf without default keybindings.
 
+    sync  synchronizes yanked/deleted files with server
     echo  prints its arguments to the message line
     cd    changes working directory to its argument
     push  simulate key pushes given in its argument

eval.go

@@ -325,6 +325,18 @@ func (e *CallExpr) eval(app *App, args []string) {
 		app.ui.sync()
 		app.ui.renew()
 		app.nav.renew(app.ui.wins[0].h)
+	case "sync":
+		list, copy, err := loadFiles()
+		if err != nil {
+			msg := fmt.Sprintf("sync: %s", err)
+			app.ui.message = msg
+			log.Printf(msg)
+			return
+		}
+		app.nav.saves = make(map[string]bool)
+		for _, f := range list {
+			app.nav.saves[f] = copy
+		}
 	case "echo":
 		app.ui.message = strings.Join(e.args, " ")
 	case "cd":