ENH: Allow --no option for towncrier

This allows to not delete files, which can be useful when
creating release note documents during a CI step, e.g. for
non-final documentation.

The `--yes` and `--no` options given both lead to `--no` right now,
although that seems not like a big issue.

src/towncrier/__init__.py

@@ -45,10 +45,17 @@ def _get_date():
 @click.option(
     "--yes",
     "answer_yes",
-    default=False,
+    default=None,
     flag_value=True,
     help="Do not ask for confirmation to remove news fragments.",
 )
+@click.option(
+    "--no",
+    "answer_yes",
+    default=None,
+    flag_value=False,
+    help="Do not remove news fragments and do not ask whether or not to remove.",
+)
 def _main(draft, directory, project_name, project_version, project_date, answer_yes):
     return __main(
         draft, directory, project_name, project_version, project_date, answer_yes

src/towncrier/_git.py

@@ -11,15 +11,20 @@ def remove_files(fragment_filenames, answer_yes):
     if not fragment_filenames:
         return
 
-    if answer_yes:
+    if answer_yes is None:
+        click.echo("I want to remove the following files:")
+    elif answer_yes:
         click.echo("Removing the following files:")
     else:
-        click.echo("I want to remove the following files:")
+        click.echo("Keeping the following files:")
 
     for filename in fragment_filenames:
         click.echo(filename)
 
-    if answer_yes or click.confirm("Is it okay if I remove those files?", default=True):
+    if answer_yes is None:
+        answer_yes = click.confirm("Is it okay if I remove those files?", default=True)
+
+    if answer_yes:
         call(["git", "rm", "--quiet"] + fragment_filenames)