Search for the selected text

[The `*` command][star] searches for the word under the cursor. That makes sense in Normal mode, but from Visual mode it would be more useful if the star command searched for the current *selection*, rather than the current word. We can add this feature to Vim using the [visual star search plugin][visual-star].

[visual-star]: https://github.com/nelstrom/vim-visual-star-search
[star]: http://vimdoc.sourceforge.net/htmldoc/pattern.html#star