Add libcurl support for tls_server_example and no_tls_server_example

[peter279k]

As title, it should add the cURL client to send POST request on IEC-61850 servers when IEC-61850 client sends on/off message.

[peter279k]

It should install libcurl4-openssl-dev package on Ubuntu 18.04.

[peter279k]

• JSON process C library
  • https://www.cnblogs.com/wybliw/p/10462708.html
  • https://gist.github.com/alan-mushi/19546a0e2c6bd4e059fd
  • https://lightder.github.io/2017/09/15/json-c-example/

[peter279k]

• libcurl library usage
  • https://gist.github.com/whoshuu/2dc858b8730079602044
  • https://curl.se/libcurl/c/getinmemory.html
• libcurl using dynamic/static link library
  • https://www.matteomattei.com/how-to-cross-compile-curl-library-with-ssl-and-zlib-support/

[peter279k]

JSON-CMake module file

• https://github.com/fastogt/cmake/blob/master/FindJSON-C.cmake
• https://github.com/eclipse/mraa/blob/master/cmake/modules/FindJSON-C.cmake
• https://stackoverflow.com/questions/20746936/what-use-is-find-package-if-you-need-to-specify-cmake-module-path-anyway

[peter279k]

Another C file stuffs

• https://riptutorial.com/c/example/3250/calling-a-function-from-another-c-file