Add jsonpb option to disable HTML scaping

[antoniomo]

Helps fixing:

• Disable HTML Escaping in jsonpb? #484
• Path parameters can't have URL encoded values grpc-ecosystem/grpc-gateway#566 via
  https://github.com/gogo/gateway

Upstream issue: golang/protobuf#409

Original upstream patch by Paul Nichols (@pauln) here:
golang/protobuf#409

[johanbrandhorst]

Hm, I can see that this wasn't merged upstream, so should we really merge this here?

[antoniomo]

I guess it depends on the desired solution for #484?

As an alternative it can live as an external package, as a gogo/protobuf/jsonpb replacement. The caveat is that it makes it harder to use with other packages that just go "here" for the gogo jsonpb functionality.

[johanbrandhorst]

I guess it depends on the desired solution for #484?

As an alternative it can live as an external package, as a gogo/protobuf/jsonpb replacement. The caveat is that it makes it harder to use with other packages that just go "here" for the gogo jsonpb functionality.

Thanks for the explanation. I'm not super experienced with managing this repo, so I'm going to err on the side of caution and reject this PR for now. Could you update the issue with link to your own solution for those looking for an answer? Thanks and sorry for the silence on this PR and inconvenience.

[antoniomo]

No problem, that's understandable. I'll keep my fork with the branch so other's can use this PR as reference workaround, and perhaps keep a standalone jsonpb package with just the jsonpb code.