Fixes for some of the errors known at compile time

[vinsec]

1. Add the missing static libraries and move them into nrf_sdks. Accordingly,the Makefiles have been updated.

2.The command mergehex is not usually installed in advance.A README.md has been added in order to make the compilation process smoother.

All these changes have been carefully validated.

The compiling environment is :

Linux 4.18.0-16-generic Ubuntu 18.04.1 x86_64
GNU Arm Embedded Toolchain: 6-2017-q2-update
nRF5 SDK: nRF5_SDK_v15.2.0_9412b96

[caizelin]

@vinsec micro-ecc library is in the folder <nRF5 SDK path>/external/micro-ecc. Just change to the directory and run ./build_all.sh or .\build_all.bat. So, I think it is better to add a tutorial for this step rather than adding the pre-build libs.

[vinsec]

@vinsec micro-ecc library is in the folder <nRF5 SDK path>/external/micro-ecc. Just change to the directory and run ./build_all.sh or .\build_all.bat. So, I think it is better to add a tutorial for this step rather than adding the pre-build libs.

That would be better :)