Allow mark to accept multiple timestamps

If there is a list of migrations that needs to be marked as completed
(or not completed or deferred), we currently have to do:

```
dbmigrator mark -t 20160228212456
dbmigrator mark -t 20160228202637
```

Now it will accept a list and we can do this instead:

```
dbmigrator mark -t 20160228212456 20160228202637
```

dbmigrator/commands/mark.py

@@ -14,32 +14,34 @@
 
 
 @utils.with_cursor
-def cli_command(cursor, migrations_directory='', migration_timestamp='',
+def cli_command(cursor, migrations_directory='', migration_timestamps=None,
                 completed=None, **kwargs):
     if completed is None:
         raise Exception('-t, -f or -d must be supplied.')
 
     migrations = {version: migration
                   for version, _, migration in utils.get_migrations(
                       migrations_directory, import_modules=True)}
-    migration = migrations.get(migration_timestamp)
-    if migration is None:
-        raise SystemExit(
-            'Migration {} not found'.format(migration_timestamp))
-
-    utils.mark_migration(cursor, migration_timestamp, completed)
-    if not completed:
-        message = 'not been run and not deferred'
-    elif completed == 'deferred':
-        message = 'deferred'
-    else:
-        message = 'completed'
-    logger.info('Migration {} marked as {}'.format(migration_timestamp,
-                                                   message))
+
+    for migration_timestamp in migration_timestamps:
+        migration = migrations.get(migration_timestamp)
+        if migration is None:
+            raise SystemExit(
+                'Migration {} not found'.format(migration_timestamp))
+
+        utils.mark_migration(cursor, migration_timestamp, completed)
+        if not completed:
+            message = 'not been run and not deferred'
+        elif completed == 'deferred':
+            message = 'deferred'
+        else:
+            message = 'completed'
+        logger.info('Migration {} marked as {}'.format(migration_timestamp,
+                                                       message))
 
 
 def cli_loader(parser):
-    parser.add_argument('migration_timestamp')
+    parser.add_argument('migration_timestamps', nargs='+')
     parser.add_argument('-t', action='store_const',
                         const=True,
                         dest='completed',

dbmigrator/tests/test_cli.py

@@ -192,6 +192,12 @@ def test_multiple_contexts(self):
 
 
 class MarkTestCase(BaseTestCase):
+    def test_missing_version(self):
+        cmd = ['--db-connection-string', testing.db_connection_string]
+
+        with self.assertRaises(SystemExit) as cm:
+            self.target(cmd + ['mark', '-t'])
+
     def test_missing_t_f_d_option(self):
         cmd = ['--db-connection-string', testing.db_connection_string]
 
@@ -221,6 +227,24 @@ def test_mark_as_true(self):
         self.assertIn('20160228202637   add_table         False', stdout)
         self.assertIn('20160228212456   cool_stuff        True', stdout)
 
+    def test_mark_more_than_one(self):
+        testing.install_test_packages()
+        cmd = ['--db-connection-string', testing.db_connection_string]
+
+        self.target(cmd + ['--context', 'package-a', 'init', '--version', '0'])
+        self.target(cmd + ['--context', 'package-a',
+                           'mark', '-t', '20160228212456', '20160228202637'])
+
+        logger.info.assert_called_with(
+            'Migration 20160228202637 marked as completed')
+
+        with testing.captured_output() as (out, err):
+            self.target(cmd + ['--context', 'package-a', 'list'])
+
+        stdout = out.getvalue()
+        self.assertIn('20160228202637   add_table         True', stdout)
+        self.assertIn('20160228212456   cool_stuff        True', stdout)
+
     def test_mark_as_true_already_true(self):
         testing.install_test_packages()
         cmd = ['--db-connection-string', testing.db_connection_string]