implement delete-snapshot function in snapshot package.

src/snapshot.lisp

@@ -6,7 +6,8 @@
         #:nera)
   (:export
    #:take-snapshot
-   #:restore-from-snapshot))
+   #:restore-from-snapshot
+   #:delete-snapshot))
 (in-package #:snapshot)
 
 (defun take-snapshot ()
@@ -31,3 +32,6 @@ user can repopulate that database after they have restored this website. The
   (format t "RESTORE-FROM-SNAPSHOT NOT IMPLEMENTED."))
 
 
+(defun delete-snapshot (snapshot-name)
+  "Deletes the snapshot in the /snapshots directory with `SNAPSHOT-NAME'."
+  (storage:remove-raw-directory (format nil "snapshots/~a/" snapshot-name)))