Removes IO modules from Daru

[athityakumar]

Through this PR, I'd like to safely port away all IO modules of Daru, keeping the Marshalling methods intact. I'll request a review in a couple of days.

[athityakumar]

@zverok - Ready for a review 😄

Edit : I'll fix the merge conflicts while fixing the above review comments.

[athityakumar]

@zverok - Opened #434 for noting down the dependency issue. Can you add it into the milestone to keep track?

[zverok]

Done.

[v0dro]

This needs a serious relook and separating IO from the core gem should be seriously considered before the next major release.