Bootloader infrastructure and main logic (#404)

* adds bootloader code without a SHA256 implementation

* small fixes and typos

bootloader/Cargo.toml

@@ -0,0 +1,28 @@
+[package]
+name = "bootloader"
+version = "0.1.0"
+authors = [
+  "Fabian Kaczmarczyck <kaczmarczyck@google.com>",
+]
+build = "build.rs"
+license = "Apache-2.0"
+edition = "2018"
+
+[dependencies]
+byteorder = { version = "1", default-features = false }
+cortex-m = "^0.6.0"
+cortex-m-rt = "*"
+cortex-m-rt-macros = "*"
+panic-abort = "0.3.2"
+rtt-target = { version = "*", features = ["cortex-m"] }
+
+[profile.dev]
+panic = "abort"
+lto = true
+opt-level = 3
+
+[profile.release]
+panic = "abort"
+lto = true
+# Level "z" may decrease the binary size more of necessary.
+opt-level = 3