fcry - [f]ile[cry]pt - initial commit (alpha 0.9.0)

A file en-/decryption tool for easy use.

Currently `fcry` uses `ChaCha20Poly1305` ([RFC 8439](https://datatracker.ietf.org/doc/html/rfc8439)) as [AEAD](https://en.wikipedia.org/wiki/Authenticated_encryption) cipher provided by the [chacha20poly1305](https://docs.rs/chacha20poly1305/latest/chacha20poly1305/) crate.

src/utils.rs

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-3.0-only
+use std::{
+    fs::File,
+    io::{self, Read, Write},
+};
+
+pub(crate) fn read_from_file_or_stdin<S: AsRef<str>>(input_file: Option<S>) -> Box<dyn Read> {
+    match input_file {
+        Some(f) => Box::new(File::open(f.as_ref()).unwrap()),
+        None => Box::new(io::stdin()),
+    }
+}
+
+pub(crate) fn write_to_file_or_stdout<S: AsRef<str>>(output_file: Option<S>) -> Box<dyn Write> {
+    match output_file {
+        Some(f) => Box::new(File::create(f.as_ref()).unwrap()),
+        None => Box::new(io::stdout()),
+    }
+}