Consider making conversions a commonjs module

[daedalus28]

And then importing from index so that we can do the dynamic reduce thing but still have them as top level exports

[daedalus28]

The plan is to export F.indexed, F.mutable, and possibly F.flipped (although we might just deprecate all flips as per #166). These exports are at the top of the conversions file and just need to be renamed and exported: https://github.com/smartprocure/futil-js/blob/master/src/conversion.js#L4-L6

[daedalus28]

It looks like we are going to export indexed and mutable, but flipped is too close to flip - especially after #283 which would add a flips. Trying to remember the difference between flip, flips, and flipped sounds like it would make most developers flip out.