Fixes #915

The `Respecting .gitignore` link pointed to a section of the readme which no longer exists.

- https://github.com/sharkdp/fd
- https://mike.place/2017/fzf-fd/

/cc @williamsmj

On Cygwin and MinGW, the fzf binary will have a .exe extension, so
ignore that binary if it exists as well as the bare binary.

Since https://github.com/BurntSushi/ripgrep/issues/200 is fixed in
0.7.1, we can safely suggest ripgrep as the candidate generator as it
has a more precise implementation of gitignore filtering than the silver
searcher.

When `ps` is aliased for something uncommon, like `alias ps=grc ps` which colorizes ps output, the output of `ps` can be unexpected and/or undesired.

This change makes ps to be always executed as command, even if it's aliased.

Reference: http://zsh.sourceforge.net/Doc/Release/Shell-Builtin-Commands.html

> The flag -r reverses the order of the events

Handles records like "[20.20.7.168]:9722 ssh-rsa ..."

This is a standard format for servers running on custom port according to http://man.openbsd.org/sshd.8#SSH_KNOWN_HOSTS_FILE_FORMAT

    A hostname or address may optionally be enclosed within ‘[’ and ‘]’
    brackets then followed by ‘:’ and a non-standard port number.

Related: #1072
/cc @janlazo

/cc @chrisjohnson

Close #1067
Close #1083

Close #1018

Run the command as is in cmd.exe with no parsing and escaping.
Explicity set cmd.SysProcAttr so execCommand does not escape the command.
Technically, the command should be escaped with ^ for special characters,
including ". This allows cmd.exe commands to be chained together.

See https://github.com/neovim/neovim/pull/7343#issuecomment-333350201

This commit also updates quoteEntry to use strings.Replace instead of
strconv.Quote which escapes more than \ and ".

* Don't do shell quoting for weird chars

This would prevent tabs from being escaped as `$'\t'` (definitely not what I would want to see as initial value in the search).

* Do different escape.

Close #1060

Close #1066
Close #1068

Close #1055

- Use bash for `set -o pipefail`
- Fall back to simpler find command when the original command failed

Related: #1061

Remove code that is no longer relevant after the removal of ncurses
renderer. This commit also fixes background color issue on tcell-based
FullscreenRenderer (Windows).

This fixes foreground color inside preview window when the text has ANSI
attributes except for foreground color.

Close #1046

Close #1046

Prevents the following case:
before pathshorten - /usr/bin
after pathshorten - /u/bin
piped to cmd.exe - U:/bin

Port of https://github.com/junegunn/fzf.vim/commit/e7928d154aad71e530daf5c17733275da5732680

Since :FZF does not enable preview window, we determine based on full
&columns instead of &columns / 2.

Temporary workaround for non-Windows environment

Reference:
https://github.com/vim/vim/issues/1998
https://github.com/junegunn/fzf/pull/1019#issuecomment-327008348

IMPORTANT:
cmd.exe and powershell are fine in default Windows terminal.
cmd.exe prompt is broken on ConEmu because it natively supports ucs-2 only.
utf-16 support is exclusive to .Net (ie. powershell).
utf-8 supports requires chcp, external program, but does not fix the cmd.exe prompt.
Use powershell on ConEmu to avoid corrupted text on display

Requirements:
- compiled with +terminal
- has patch-8.0.995
- has('gui_running') returns 1

Original Patch: https://github.com/junegunn/fzf/commit/a9bf29b65ec36d9caa7298aad0322fba8cb3e130

Close #1040