Added debug=2 in release profile to all examples.

This makes rtt output work right when using `cargo run` in release mode.

Debug was already enabled for release builds in some of the examples but
not all.

examples/std/Cargo.toml

@@ -23,3 +23,6 @@ clap = { version = "3.0.0-beta.5", features = ["derive"] }
 rand_core = { version = "0.6.3", features = ["std"] }
 heapless = { version = "0.7.5", default-features = false }
 static_cell = { version = "1.1", features = ["nightly"]}
+
+[profile.release]
+debug = 2