Add ColorHeaderAndFields logger option

[picatz]

This PR builds on #108, extending the ability to color fields as well as the level header.

When I have log lines with multiple fields (especially with long values), I find it hard to visually pinpoint the part of the log message I'm interested in. I think by dimming the key= part of the field, it'll be faster and easier to visually parse the information. For multi-line values, this will also dim the | prefix.

Usage

log := hclog.New(&hclog.LoggerOptions{
	Color:                hclog.AutoColor,
	ColorHeaderAndFields: true,
})

Note: if ColorHeaderOnly is also set as true, that takes precedence.

Before

After

[evanphx]

Mostly a lot of questions about formatting and logic

[evanphx]

It seems weird to use faint and bold. Why not just bold?

[picatz]

I feel like faint helps break up a log line visually, for me, better than just bold.

Just Bold

Bold and Faint

[evanphx]

The concern is mostly how other folks default terminal fonts will handle faint+bold. We have to be careful picking here because it has a big influence on all the users.

[picatz]

That's a fair point. I think the Windows terminal would likely be the odd one to consider, and it seems like they do support this style: microsoft/terminal#6703 (comment)

Faint/dim is a fairly standard SGR style, implemented in VSCode's terminal emulator (xtermjs) as well (which is what those screenshots are showing).

Bold, I believe, is the more widely supported style. But, I would really rather have faint than bold here to help break up the line. I feel it's important. I don't know if we can actually detect if it's supported?

[evanphx]

Looks great! Be sure to squash the history on merging. One minor question about fainting the = is all.