Add PID and TID to the JSON output

[vini-fda]

For context, see issue #29.

This is my proposed solution as an attempt to write the "proper" PID and TID of the results so that the processes/threads can be differentiated.

• The process id is retrieved using std::process::id(), which "Returns the OS-assigned process identifier associated with this process.", as documented in the Rust official docs
• The thread id is retrieved as std::thread::current().id() , which could be problematic, as I've made a hack to convert the debug output to an int, and there's no guarantee that the integer is related to the OS's assigned identifier of the thread. A proper solution would depend on the stabilization of ThreadId::as_u64. However, as the purpose here is only to uniquely identify a thread(which is already guaranteed by the current API), I don't think this is a major issue.

[Wumpf]

Thank you so much for looking into it and documenting everything so well in the issue & PR!

[Wumpf]

sweet. Thank you!