Ref #790

Close #799

Close #798

Excerpt from http://www.tldp.org/HOWTO/Bash-Prompt-HOWTO/x361.html:

> - Save cursor position:
>   \033[s
> - Restore cursor position:
>   \033[u
>
> The latter two codes are NOT honoured by many terminal emulators. The
> only ones that I'm aware of that do are xterm and nxterm - even though
> the majority of terminal emulators are based on xterm code. As far as
> I can tell, rxvt, kvt, xiterm, and Eterm do not support them. They are
> supported on the console.

They are also unsupported by Neovim terminal.

Fix line wrapping in preview window

Close #790

Close #791

- Use noshellslash for strict path expansion in fzf#run and s:cmd
  (shellescape depends on shellslash)
- Double-quote the fzf command for cmd.exe
- Add fzf#shellescape to encapsulate the logic
- Close #786

_fzf_completion_loaded is no longer checked. This change increases the
load time by a few milliseconds, but I can't think of a better way to
handle the issue.

Close #783.

This removes the need for the 'sed' call. Faster, cleaner.

With a `bufhidden=wipe` buffer (e.g. vim-startify) the buffer would not
exist anymore, resulting in an error.

Close #774

Replace the "temp file" workaround with the "read" function: it's
simpler and faster.

Use proper escaping, remove the custom function.

The "file" widget uses last token as root for the "find" command.
This replaces the equivalent of '**' completion in bash/zsh.
The "$dir" non-expanded variable can be used in FZF_CTRL_T_COMMAND to
set the root.

Close https://github.com/junegunn/fzf.vim/issues/265

Add `:wrap` to --preview-window to wrap lines instead

Close #756