Added '-a' (--append) arg to append a line of text to the notes file.

https://github.com/pubs/pubs/issues/200

pubs/commands/note_cmd.py

@@ -10,6 +10,7 @@ def parser(subparsers, conf):
                                    help='edit the note attached to a paper')
     parser.add_argument('citekey', help='citekey of the paper',
                         ).completer = CiteKeyCompletion(conf)
+    parser.add_argument('-a', '--append', help='append a line of text to the notes file', default=None)
     return parser
 
 
@@ -18,7 +19,12 @@ def command(conf, args):
     ui = get_ui()
     rp = repo.Repository(conf)
     citekey = resolve_citekey(rp, args.citekey, ui=ui, exit_on_fail=True)
+    append = args.append
     notepath = rp.databroker.real_notepath(citekey, rp.conf['main']['note_extension'])
-    ui.edit_file(notepath, temporary=False)
+    if append is None:
+        ui.edit_file(notepath, temporary=False)
+    else:
+        with open(notepath, 'a') as fd:
+            fd.write(append)
     NoteEvent(citekey).send()
     rp.close()