When changing focus away and back to vim while in the middle of editing
the command-line, vim-tmux-focus-events emits errors from the function
called by the `:cnoremap` mappings. This patch replaces these mappings
with a call to `do#sink()` which does nothing. Simply removing the
mappings will result in `<F24><F25>` being inserted on the command-line
since tmux will send this text when `tmux set-option -g focus-events
on`, this is why `do#sink()` is needed.
vim-gitgutter is buggy. vim-signify might be better, it does allow
configuration of which events trigger a sign column update and this
patch takes advantage of that. Firstly, the `CursorHold` and
`CursorHoldI` events are disabled and replaced with `InsertLeave` and
`TextChanged` events. This makes the sign column updates immediate, and
since vim-signify is asynchronous it's faster too.
Previously the `autocmd` to replace the date on the first line if `Last
change: ` was present resulted in the cursor being moved in non `help`
filetypes due to the substitution failing. Now the substitution is only
attempted if the current file is a `help` file.
