C library for STM32 with emgo

**Feature description**

C library for STM32 MCU

**Is your feature request related to a problem? Please describe.**
It is not possible to run the library in `lib/cgo` on MCU .

**Describe the solution you'd like**

Use [emgo](https://github.com/ziutek/emgo) to transpile `skycoin/skycoin` library code to C , then link binaries for STM32 platform

**Describe alternatives you've considered**
All other alternatives for compiling with go for MCU in the end rely on Firmata, which does not fit in our use case scenario.

**Additional context**
Ideally this could be used to upgrade the cipher library used in `skycoin/hardware-wallet`. Priority consists in support for [`STM32F4` series](https://en.wikipedia.org/wiki/STM32#STM32_F4).

**Possible implementation**

- [ ] Transpile `skycoin/skycoin` library code to C using [emgo](https://github.com/ziutek/emgo) .
- [ ] Link against [library for STM32](https://github.com/ziutek/emgo/tree/master/egpath/src/stm32)
- [ ] Parameterize the test suite (if needed) so as to test multiple implementations
- [ ] Execute the current test suite by calling the binaries obtained in aforementioned steps