docs: Revive 0.35 examples (#121)

## Description

Add back the examples that were removed when moving from 0.35 to 0.9x.

## Breaking Changes

None

## Notes & open questions

How much should we bikeshed the progress reporting in the examples,
using console and indicatif crates? On the one hand it is nice, on the
other hand it makes the examples more complex.

I think we might put basic progress display for import, download and
export into the util crate. But I think it would be nice if we could get
by without the `--features exampes` feature flag for most or all
examples, so maybe not use console and indicatif so we don't have to
have it as dev dependencies.

I changed the transfer example to use clap like the other examples. I
hope you don't mind, @matheus23.

## Change checklist

- [ ] Self-review.
- [ ] Documentation updates following the [style
guide](https://rust-lang.github.io/rfcs/1574-more-api-documentation-conventions.html#appendix-a-full-conventions-text),
if relevant.
- [ ] Tests if relevant.
- [ ] All breaking changes documented.

Implements #120
Implements #117

---------

Co-authored-by: Philipp Krüger <[email protected]>

Author: rklaehn

Cargo.lock

@@ -58,6 +58,7 @@ testresult = "0.4.1"
 tracing-subscriber = { version = "0.3.19", features = ["fmt"] }
 tracing-test = "0.2.5"
 walkdir = "2.5.0"
+iroh = { version = "0.90", features = ["discovery-local-network"]}
 
 [features]
 hide-proto-docs = []

Cargo.toml

@@ -0,0 +1,35 @@
+#![allow(dead_code)]
+use anyhow::Result;
+use iroh::SecretKey;
+use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt, EnvFilter};
+
+/// Gets a secret key from the IROH_SECRET environment variable or generates a new random one.
+/// If the environment variable is set, it must be a valid string representation of a secret key.
+pub fn get_or_generate_secret_key() -> Result<SecretKey> {
+    use std::{env, str::FromStr};
+
+    use anyhow::Context;
+    use rand::thread_rng;
+    if let Ok(secret) = env::var("IROH_SECRET") {
+        // Parse the secret key from string
+        SecretKey::from_str(&secret).context("Invalid secret key format")
+    } else {
+        // Generate a new random key
+        let secret_key = SecretKey::generate(&mut thread_rng());
+        println!(
+            "Generated new secret key: {}",
+            hex::encode(secret_key.to_bytes())
+        );
+        println!("To reuse this key, set the IROH_SECRET environment variable to this value");
+        Ok(secret_key)
+    }
+}
+
+// set the RUST_LOG env var to one of {debug,info,warn} to see logging info
+pub fn setup_logging() {
+    tracing_subscriber::registry()
+        .with(tracing_subscriber::fmt::layer().with_writer(std::io::stderr))
+        .with(EnvFilter::from_default_env())
+        .try_init()
+        .ok();
+}