Enabled `exclude-dir` to allow specifying multiple directories

[sadakatsu]

I needed to specify more than one directory to ignore. The following commit allows specifying multiple directories using either commas or semicolons as separators. It provides the expected results locally.

[wimgoeman]

I agree with the handling of the multiple exclude dirs. It is nice to have that option. The suppression of the lib includes however I do not really see the value of. Having them in the output file should not hinder compilation. I can understand the output file is 'cleaner' without them, but there is no real value of having a clean output file. I'd prefer to keep this utility as simple as possible...