Using os-independent libraries for filesystems paths

[kasra-keshavarz]

Often times errors like this are thrown at the user:

SystemExit: the provided output folder for EASYMORE should end with (/)

This could be avoided using os.path or pathlib libraries inside the package.

[ShervanGharari]

@kasra-keshavarz I'll be cleaning this up soon and will transition to using os.path consistently for all file read and write operations. If you have any suggestions or preferences, please let me know.