Parse proto files

[pepegar]

It would be great to have a way to parse protocol buffers in
Skeuomorph!

This task would involve several smaller tasks to be completed (we can
address each one in a separate PR if we like):

• compile the proto file into its binary format
• get a FileDescriptorProto out of it
• convert all message declarations into ProtobufF declarations.
• create a protocol describing a Protobuf file.
• create transformation between Protobuf's protocol and Mu's
  protocol.

Compile proto file

To do this we can use protoc-jar as a library.

Convert proto bytes into a FileDescriptorProto

FileDescriptorProto comes from protobuf-java library, the oficial
SDK for protobuf in Java. The idea would be to use
FileDescriptorProto.parseFrom to convert from the bytes generated
with protoc compilation into something with more semantics, like a
FileDescriptorProto.

Convert message declarations to ProtobufF

This is done with a Droste's Coalgebra, and the process would be
similar to the one we are doing for avro here.

Create a skeuomorph.protobuf.Protocol

This should be similar to Avro's.

Conversion Protobuf -> Mu

This should be similar to Mu's fromAvroProtocol

Thanks @AdrianRaFo for https://github.com/AdrianRaFo/proton, from which I pulled the inspiration to create this issue a la skeuomorph

[AdrianRaFo]

Proton uses sbt-protoc and scalapb behind the scenes to read the proto file so it can be helpful to discover how to proceed in some cases.
Thank you @pepegar

[juanpedromoreno]

This has been completed by #66