[vim keymap] Style tweaks

* simpler concat
* less escaping
* shave a line
* throw early
* throw new error
* single quotes
* format returns
* rm unneeded parens
* add whitespace
* re-add braces
[show-hint addon] Restructure

Also makes sure that no two hinting dialogs can be active at the
same time.

Issue #1619
lineCount -> lastLine
don't exit visual mode when starting on a blank line