* added multithreading crate with thread pool
* added crate mutlithreading
* replaced `threads` memeber from `Threadpool`
mutex with atomic primitive
* fixed doctest for threadpool
* added module documentation to multithreading
* added functionality to drop thread handles
automatically when threads have finished
* reformatted crate `multithreading` to pass tests
* added benchmark for `threadpool`
using `criterion`.
* finished benchmark for threadpool
and fixed documentation for threadpool
* added unit test to `multithreading`
teridax