Creates a C SDK to interact with the server

[auyer]

This PR creates a SDK in C for the MemoryKV server. It should give access to the HTTP routes in a simple manner.

I used:

• libcurl to call the HTTP endpoints from C, because it is a well known library and works on almost any system.
• CMake to make it easier to build and link the library and the example.
• clang-tidy for static analysis/linting and clang-format for formatting
• for the result struct, I wanted a Rust Result feeling, and took inspiration from this gist: https://gist.github.com/f0rki/9b2c2b73d46ccdad2b39ab79b3a5517f

I had not used C for a long time. It was fun!

Code Review

I asked for a code review in codereview.stackexchange.com and got a great response, that helped me improve this code. Thanks Harith !

https://codereview.stackexchange.com/questions/287460/small-http-client-sdk-created-using-libcurl-in-c-language/