Always highlight current match after star-search

This aims to fix the second half of #3.

One potential issue: consider some text with overlapping matches, e.g. `a a a`.

Currently, `*` in visual mode with the second 2 a's selected (i.e. `a [a a]`) will result in `Search` highlighting `[a a] a` and `ObliqueCurrentMatch` highlighting `a [a a]` (and shadowing `Search`, so `Search` is really only visible for `[a ]a a`).

The new behavior would be to highlight `[a a] a` with `ObliqueCurrentMatch` (and of course `Search` under that, but invisible). Thus the current match is not the original selection, but it is the leftmost non-overlapping match, i.e. what would be jumped to with `n` or `N`.

This scenario seems rather obscure, however, so I'm not sure whether it matters much.