Add solana-keygen

Same as solana-mint, but without a tokens field.

src/bin/keygen.rs

@@ -0,0 +1,14 @@
+extern crate ring;
+extern crate serde_json;
+
+use ring::rand::SystemRandom;
+use ring::signature::Ed25519KeyPair;
+use std::error;
+
+fn main() -> Result<(), Box<error::Error>> {
+    let rnd = SystemRandom::new();
+    let pkcs8_bytes = Ed25519KeyPair::generate_pkcs8(&rnd)?;
+    let serialized = serde_json::to_string(&pkcs8_bytes.to_vec())?;
+    println!("{}", serialized);
+    Ok(())
+}