Use Pathlib Library to Handle Filepaths

[r0bc94]

This PR intruduces the pathlib library to handle filepaths.

The obvious adavantage of this is, that now the path handling is transparent between different operation systems (such as windows and linux). This also makes the script work on windows systems (if ghostscript is installed and the path to the gswin64 binary is registered in %PATH%).

Note: Since im currently not able to test it in linux, I've only tested this changes in windows. Before merging you should therefore check, if this script still works fine in linux.

Fixes #4

[r0bc94]

Sorry about the forced updates, I actually missed that there is a develop branch, so I rebased my branch to match the develop's state. However it seems that your master branch is actually some commit before your develop branch which confused me a bit :). This state should be fine now.

However, I would fix the issue that your develop branch is before master. If you fixed it please let me know, which branch I should use as a target for this PR.

[r0bc94]

I also just disabled the checks for invalid characters in the input- and output's filename since i'm not sure if this check is still needed in order for ghostscript to work properly.