Refactoring: remove helpers.get_abspath()

[truth-quark]

The helpers.get_abspath() function is not required once #40 is complete:

• sys.exit() calls from the custom logging module are being removed
• Refactoring to exceptions means get_abspath() throws IOError if files are missing (duplicating Python's functionality).
• The function is only used 2x

[atteggiani]

Hmm yes that is true, but the helpers.get_abspath() function might still be needed to get the path we want logged. I think Python's IOError does not necessarily output the absolute path, but whatever argument was given as a path.

[truth-quark]

Ooops, Python throws a FileNotFound error which shows the path (abs or relative, whichever is passed to the func). This is fine as um2nc doesn't change the working directory.

[atteggiani]

Yeah, I created the get_abspath() function to log the absolute paths. Even though um2nc does not change working directory, I usually prefer working with absolute paths in general.

[truth-quark]

In the interest of simplicity, I recommend going with a minimal implementation, deferring to Python defaults etc. Each specialisation, additional code branching etc contributes to more complexity, more testing and so forth. The less code we have, the easier it is for different devs to understand & maintain :-)

[atteggiani]

Yes that makes sense. Well, for now we can remove it, then if we need a way to work with absolute paths we will reinstate it.

However, if we remove it, we neeed a function to check existence of files and directories to replace the logic of the check and checkdir input arguments to get_abspath().