Overhaul the `%current-suggestion` API

[aartaka]

One thing that I'd change before 3.0 is %current-suggestion. It's numbers and offsets, and it's a really inconsistent API, so making current suggestion to actually be a suggestion instead and indexing based on source contents. eq list search is cheap, mental juggling to work with indices is expensive.

Originally posted by @aartaka in #29 (comment)