use unistd.h's chdir() for updating the current working directory

[kasrasadeghi]

unistd.h is not standard, so i'd be locking out windows (for now) by doing this.

[kasrasadeghi]

I'm going to use unistd.h for directory management and only use std::filesystem for traversal and keeping track of paths. This project is to learn the build system for unix systems better in order to prepare me for my OS class, and thus I think it's more valuable to learn standard unix ways of doing things than to learn the standard way of doing things, especially as we won't have access to the STL in that class.

[kasrasadeghi]

Woops, didn't mean to close this yet.