Return split results as arrayref instead of list

In 0caac1347e2e3f2fc290f0a4ffc0281b5df68abb I accidentally changed
the return behavior from arrayref to list, which worked fine, but
could be slower when large lists are returned and in any case was an
unintended change.
Merge pull request #20 from jonjensen/split-518-return-arrayref

Return split results as arrayref instead of list