Mark exercises as new. Fixes #66

When fetching new exercises, it's helpful to have an indicator of which
exercise you have not yet submitted any code for, especially since the
exercises are now listed in alphabetical order, not in any particular
order of completion.

assignment.go

@@ -8,9 +8,10 @@ import (
 )
 
 type Assignment struct {
-	Track string
-	Slug  string
-	Files map[string]string
+	Track   string
+	Slug    string
+	Files   map[string]string
+	IsFresh bool `json:"fresh"`
 }
 
 func SaveAssignment(dir string, a Assignment) (err error) {
@@ -35,7 +36,11 @@ func SaveAssignment(dir string, a Assignment) (err error) {
 		}
 	}
 
-	fmt.Println(a.Track, "-", a.Slug)
+	fresh := " "
+	if a.IsFresh {
+		fresh = "*"
+	}
+	fmt.Println(fresh, a.Track, "-", a.Slug)
 
 	return
 }