Standarization for deprecation message

[uilianries]

Hi!

I was working on PR #1347 and can't found a standard format for deprecation notice. What I found:

• 1 note using warning box (python 2)
• 1 note using caution box (boost build generator)
• Many inline comments [DEPRECATED]
• Conan transit is using (DEPRECATED)

Could we adopt a standard format/box/message when deprecating something?

[danimtb]

Normally we use [DEPRECATED] for inlined and maybe just use the caution box for deprecated things

[uilianries]

Yeah, but for what specific cases? Maybe I should use [DEPRECATED] for no_proxy since it's not real important thing like Python 2, right?

[danimtb]

It depends if there is a need for an additional message or not. But yeah, for small things, just use [deprecated]