Improve file error handling

[jasbrake]

Current Behavior

If you call the program without a file parameter, it will try to resolve the filepath of '' (empty string) and fail.

What it should do

It should: let the user know that they need to pass in a file path as a parameter in order to run it.

Also

Similarly, I need to decide whether it is best to leave File not found errors unhandled, or print a friendly error message and exit.