Add protobuf support

[denysvitali]

[coveralls]

Pull Request Test Coverage Report for Build 1069

• 1 of 63 (1.59%) changed or added relevant lines in 11 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.2%) to 21.478%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pippo-content-type-parent/pippo-csv/src/main/java/ro/pippo/csv/CsvEngine.java	0	1	0.0%
pippo-content-type-parent/pippo-fastjson/src/main/java/ro/pippo/fastjson/FastjsonEngine.java	1	2	50.0%
pippo-content-type-parent/pippo-snakeyaml/src/main/java/ro/pippo/snakeyaml/SnakeYamlEngine.java	0	1	0.0%
pippo-content-type-parent/pippo-xstream/src/main/java/ro/pippo/xstream/XstreamEngine.java	0	1	0.0%
pippo-core/src/main/java/ro/pippo/core/TextPlainEngine.java	0	1	0.0%
pippo-content-type-parent/pippo-jackson/src/main/java/ro/pippo/jackson/JacksonBaseEngine.java	0	3	0.0%
pippo-core/src/main/java/ro/pippo/core/route/DefaultRouteContext.java	0	4	0.0%
pippo-content-type-parent/pippo-protobuf/src/main/java/ro/pippo/protobuf/ProtobufInitializer.java	0	5	0.0%
pippo-content-type-parent/pippo-jaxb/src/main/java/ro/pippo/jaxb/JaxbEngine.java	0	9	0.0%
pippo-core/src/main/java/ro/pippo/core/Response.java	0	9	0.0%
<!--	Total:	1	63

Files with Coverage Reduction	New Missed Lines	%
pippo-core/src/main/java/ro/pippo/core/Response.java	1	15.56%
<!--	Total:	1

Totals
Change from base Build 1068:	-0.2%
Covered Lines:	1392
Relevant Lines:	6481

---

💛 - Coveralls

[decebals]

Interesting. This PR is a particular case of #407. I will push my work on GitHub in a separate branch to make my work public.

[denysvitali]

Does my work look good? I think this may solve #407 as well, as you said :+1:

[denysvitali]

I use it like this, where LoginResponse obviously is a Protobuf Message:

ctx.status(HttpStatus.OK_200);
if(req.getUsername().equals("user") && req.getPassword().equals("password")){
resp = LoginResponse.newBuilder()
      .setSuccess(true)
      .setMessage("Login successful")
      .build();
  ctx.protobuf().send(resp);
} else {
  resp = LoginResponse.newBuilder()
      .setSuccess(false)
      .setMessage("Invalid username/password")
      .build();
  ctx.protobuf().send(resp);
}

[decebals]

Does my work look good? I think this may solve #407 as well, as you said

I will do an evaluation and I will come with a response. Thanks!