Add the stdio backend

This patch adds the stdio backend which acts as a fallback backend and
uses standard input and output.  For password queries, the rpassword
crate is used to suppress output.  Also, default_backend is changed to
return Stdio if Dialog is not available.

1 files changed, 13 insertions, 0 deletions

diff --git a/examples/backend-stdio.rs b/examples/backend-stdio.rs
new file mode 100644
index 0000000..6dbeb8d
--- /dev/null
+++ b/examples/backend-stdio.rs
@@ -0,0 +1,13 @@
+// Copyright (C) 2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
+use dialog::backends;
+use dialog::DialogBox;
+
+fn main() -> dialog::Result<()> {
+    let backend = backends::Stdio::new();
+
+    dialog::Message::new("This is a message.")
+        .title("And this is a title:")
+        .show_with(&backend)
+}