feat: add deprecation notice interface

[caarlos0]

as discussed in another issue

this would allow, for example, goreleaser, to set its own deprecation notice "provider" to nfpm...

[codecov]

Codecov Report

Merging #399 (d0b3618) into main (5e665bd) will increase coverage by 0.15%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##             main     #399      +/-   ##
==========================================
+ Coverage   65.25%   65.40%   +0.15%     
==========================================
  Files          14       15       +1     
  Lines        1842     1850       +8     
==========================================
+ Hits         1202     1210       +8     
  Misses        502      502              
  Partials      138      138              

Impacted Files	Coverage Δ
nfpm.go	80.72% <0.00%> (ø)
deb/deb.go	68.90% <100.00%> (ø)
deprecation/deprecation.go	100.00% <100.00%> (ø)

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[erikgeiser]

I intuition tells me to simplify it. What's the advantage compared to this?

var DeprecationNoticeWriter io.Writer = os.Stderr

 // Notice will notice a deprecation with the previously set noticer.
func Notice(s string) {
     DeprecationNoticeWriter.Write(s)
 }

func Noticef(format string, a ...interface{}) {
    fmt.Fprintf(DeprecationNoticeWriter, format, a...)
}

[caarlos0]

on my impl it would be easier to use, say, a logger library... but its fair, the caller can always implement a simple writer that logs...

will change it :)