feature: s<enter> repeats last search even if ; and , were reset by f/t.

- especially useful for streak-mode
doc: s<enter>
fix repeat-operation regression

- also added test to 'test' branch
fix #20: matches on last line are not highlighted
Merge branch 'master' into test
Merge branch 'test' of https://github.com/justinmk/vim-sneak into test