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

Close #357
Close #738

    TAGS=tcell make install

    printf "\x1b[38;2;100;200;250mTRUECOLOR\x1b[m\n" |
        TERM=xterm-truecolor fzf --ansi

    : | fzf --preview 'echo foo'

To build fzf with ncurses 6 on macOS:

    brew install homebrew/dupes/ncurses
    LDFLAGS="-L/usr/local/opt/ncurses/lib" make install

Also reduce the default delay to 50ms. We should not set it to 0ms as it
breaks escape sequences on WSL. If 50ms is not enough, one can increase
the delay by setting $ESCDELAY to a larger value.

Also add support for alt-[0-9] and f1[12]

`-fstype dev` is invalid. It's devfs on macOS and devtmpfs on Linux.

The updated regular expression should include not all but most of the
frequently used ANSI sequences. Close #735.