Missing support for the deprecated option

[tsl0922]

Syntax:

int32 old_field = 6 [deprecated=true];

https://blog.golang.org/godoc-documenting-go-code

Sometimes a struct field, function, type, or even a whole package becomes redundant or unnecessary, but must be kept for compatibility with existing programs. To signal that an identifier should not be used, add a paragraph to its doc comment that begins with "Deprecated:" followed by some information about the deprecation.

[paranoiacblack]

@tsl0922 Is this only a documentation enhancement? As in, whereever there is a deprecated proto field, guarantee that the generated pb.go file explicitly documents fields as "Deprecated:" like mentioned in that article. Is there something else to it?

[dsnet]

That should be it. golang/go#10909 documents "Deprecated:" as special. Tools like golint and godoc will treat deprecated specially by either warning on their usage or hiding them from documentation (golang/go#17056).