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/stm32f3/Cargo.toml

@@ -25,3 +25,6 @@ heapless = { version = "0.7.5", default-features = false }
 nb = "1.0.0"
 embedded-storage = "0.3.0"
 static_cell = { version = "1.1", features = ["nightly"]}
+
+[profile.release]
+debug = 2