Beautify help messages

[QuarticCat]

1. Add wrap_help feature to clap
2. Enable AppSettings::ColoredHelp

Before:

After:

[ducaale]

The help looks much nicer now, thanks.

[blyxxyz]

Very pretty!

Can you check if generate.sh still works? I'm worried help2man will get confused.

[QuarticCat]

@blyxxyz It still works. By default AppSettings::ColorAuto is enabled.

[ducaale]

Generated manpages seem to be okay. This is because coloring gets disabled when output is being redirected.

However, It seems that NO_COLOR doesn't disable colored help.

[QuarticCat]

@ducaale That's weird. Because clap also uses termcolor which respects NO_COLOR, and NO_COLOR take effect on my small cli project. I'm trying to figure out what went wrong.

[QuarticCat]

OK, I found why. In clap 2.3, it implements color output through ansi_term instead of termcolor, which does not support NO_COLOR (see ogham/rust-ansi-term#68) and has no other global toggle (see ogham/rust-ansi-term#10).

I'm wondering if there is a way to inject AppSettings::ColorNever but I have to go to sleep now.

[QuarticCat]

This workaround is a bit ugly for me... Anyway, I will see your opinions tomorrow.

[blyxxyz]

After experimenting a bit I think this is the best way out. It's possible to look at termcolor's detection, but NO_COLOR is really the only piece that's missing.

One nitpick, so unicode won't matter:

Suggested change

	let mut app = if env::var("NO_COLOR").is_ok() {
	let mut app = if env::var_os("NO_COLOR").is_some() {

[QuarticCat]

@blyxxyz @ducaale Done. But I find a wrong output case:

The last case seems not handled by clap.

[blyxxyz]

Ah, that's unfortunate. It already did that, so you can ignore it for this PR if you want, and I'll look at it later. The problem seems to be that Error::with_description uses automatic color detection.

Can you target develop instead of master?

[blyxxyz]

One way this does affect generate.sh is that the terminal size now determines when long lines in the help output are split, and that's visible in xh.1.

But that doesn't affect the rendered man page so it's fine.