Custom output folder

[rafspiny]

Hi @chrismaddalena,

In light of docker support (like #26) it would be nice to being able to customize the output folder so that one can easily create a volume to persist results after executing the tool.
I already implemented this in my fork. If you think this is a reasonable thing to add (3 lines) I will make a PR.

Thanks for this tool. I find it useful : )