Colorful help (#340) and some help refactoring

[brodo]

Hello,
this PR is related to issue #340 but also does some other things.

Subcommand map is now an array of CmdInfos

• Having an array allows people to change the position of commands in the help text (maps are not ordered).
• Commands now may have a command group. (needed for the main help message but also useful for other commands with many sub-commands)

HelpText now has an AdditionalHelp field

• AdditionalHelp is displayed on the bottom of the help text. It is currently only used in the main help message, but may also be useful for other things.

There is now a --color command line flag

• Colorful can be enabled with --color
• There are no checks if stdout is a tty. If you use --color, you get color! (e.g. when someone wants to pipe it into less -R)

This PR touches a lot of files, but most changes are just simple gofmt transformations in order to switch from the Subcommand map to the Subcommand array.

Cheers from 33c3,
Julian

[whyrusleeping]

Hey @brodo, Thanks for the PR. I agree, the CLI is a bit... boring.

First off, we definitely want to separate features from refactoring. So the refactor from map to slice in subcommands should be its own PR, adding colors should be its own PR, and the additionalhelp field change needs to be its own PR.

Aside from that, we should find a way to test that the colors are rendering as expected in the sharness tests.

[Kubuxu]

In my opinion the commands can be sorted by name for the display instead of making a map? Is there a case where it wouldn't be enough?

Would it be possible to instead make the Group string part of the Cmd struct itself instead of introducing new struct?

[Kubuxu]

this package should be joined with those above, this is stdlib package

[brodo]

@whyrusleeping Ok, I'll first divide this PR into three smaller ones. All the other things then can be discussed separately in the three PRs.