Don't overwrite files without the -f/--force flag

src/main.rs

@@ -253,6 +253,7 @@ fn download(server: &str, args: DownloadArgs) -> Result<(), AviaryDownloadError>
 			.write(true)
 			.truncate(true)
 			.create(true)
+			.create_new(!args.force)
 			.open(&path)
 			.map_err(|e| match e.kind() {
 				io::ErrorKind::PermissionDenied =>

src/parse.rs

@@ -61,4 +61,8 @@ pub struct DownloadArgs {
 	///
 	/// A directory will be generated based on the name of the gallery if this is not set
 	pub output: Option<PathBuf>,
+
+	#[argh(switch, short='f')]
+	/// overwrite any existing files in the output directory
+	pub force: bool,
 }