1. change include directive path 2. change return type and argument of add_func and add_and_detach_func to std::size_t 3. change argument of add_func and add_and_detach_func to const
1. change include directive path
2. change return type and argument of add_func and add_and_detach_func to
std::size_t
3. change argument of add_func and add_and_detach_func to const

Fdhvdu/ThreadPool