See https://github.com/junegunn/fzf/pull/933#discussion_r120011934

Close https://github.com/junegunn/fzf.vim/pull/386

Also change the example binding for `unix-word-rubout` to *ctrl-w* instead of *ctrl-u*

Close #935

- Update install script to download Windows binary if $TERM == cygwin
- Unset TERM if $TERM == cygwin (#933)
- Always use cmd.exe instead of $SHELL when running commands

Make sure to consistently calculate tiebreak scores based on the
original line.

This change may not be preferable if you filter aligned tabular input on
a subset of columns using --nth. However, if we calculate length
tiebreak only on the matched components instead of the entire line, the
result can be very confusing when multiple --nth components are
specified, so let's keep it simple and consistent.

Close #926

Related: https://github.com/junegunn/fzf.vim/issues/378

Due to go std lib uses poller for os.File introducing in this commit:
https://github.com/golang/go/commit/c05b06a12d005f50e4776095a60d6bd9c2c91fac


There are two changes to watch out:
1. os.File.Fd will always return a blocking fd except on bsd.
2. os.File.Read won't return EAGAIN error for nonblocking fd.

So
For 1, we just get tty's fd in advance and then set its block mode.
For 2, we use read syscall directly to get what we wanted error(EAGAIN).

Fix issue #910.

Signed-off-by: Tw <tw19881113@gmail.com>

Close #928

    # Move cursor to the top result whenever the query string is changed
    fzf --bind change:top

Close #925

expand() may return an empty string depending on the value of
&wildignore. Since expand('<sfile>') always returns an absolute path, we
can remove expand() call here. Close #917.

https://github.com/junegunn/fzf.vim/issues/361

Preview script cannot properly determine the height of fzf finder if
`--height` option is used.

https://github.com/junegunn/fzf.vim/issues/361

Close #906