CHANGE: Functions should consistently return lists

[codereport]

For problem 16 in challenges, i_to_d . maxr max . each d_to_i sum the i_to_d function returns an integer for single digit integers but lists for integers >= 10. This is bad behaviour. We should modify to Jellyfish to have the consistent behaviour and always return lists.

[UnrelatedString]

This is not in fact the case--D outputs a singleton list as desired, but Jelly unwraps singleton lists when printing them. For accurate/unambiguous representations of values, I recommend getting in the habit of using ŒṘ.