- structure CMake project
- Add CoapClient and CoapServer
- add LICENSE
- update README

Co-authored-by: Jacopo Zorzetto <jacopo.zorzetto@mail.polimi.it>

Signed-off-by: Jacopo Zorzetto <jacopo.zorzetto@mail.polimi.it>
Signed-off-by: Francesco Pham <francesco.pham@huawei.com>