Blinky for FRDM K64F in rust with mbed

That's right mbed with rust! The mbed library consist of 2 parts - mbed API (C++ world) and mbed HAL - C layer (target + cmsis). The mbed library was built by GCC ARM, for K64F target. It's linked along with this application.

Current status

It's work in progress.

• mbed rust API in the separate module (DigitalOut will be there, not part of this app)
• use cargo for everything (+ build script if required)
• target definitions - to have a complete definition for K64F target, the PinNames or other enums/macros.
• DigitalOut should be generic - currently gpio array is set to 4 (sizeof gpio_t for K64F), either to use dynamic allocation by mbed, or rust
• to have multiple mbed targets supported
• Makefile to build mbed library (only C code)