Column Sanity

I think this PR is finally ready to be merged (+/- some things, I'm sure). It's basically an entire rewrite of the `Column` type and everything that entails. The focus for this rewrite was on speed and always forcing columns back to strict/dense version whenever possible.
is that related to the inliner warnings?
https://travis-ci.org/pellucidanalytics/framian/jobs/38959656#L137