CodeMirror: ProtoBuf mode

## ProtoBuf mode

package addressbook; message Address { required string street = 1; required string postCode = 2; } message PhoneNumber { required string number = 1; } message Person { optional int32 id = 1; required string name = 2; required string surname = 3; optional Address address = 4; repeated PhoneNumber phoneNumbers = 5; optional uint32 age = 6; repeated uint32 favouriteNumbers = 7; optional string license = 8; enum Gender { MALE = 0; FEMALE = 1; } optional Gender gender = 9; optional fixed64 lastUpdate = 10; required bool deleted = 11 [default = false]; } syntax = "proto3"; package tutorial; import "google/protobuf/timestamp.proto"; option java_package = "com.example.tutorial"; option java_outer_classname = "AddressBookProtos"; option csharp_namespace = "Google.Protobuf.Examples.AddressBook"; message Person { string name = 1; int32 id = 2; // Unique ID number for this person. string email = 3; enum PhoneType { MOBILE = 0; HOME = 1; WORK = 2; } message PhoneNumber { string number = 1; PhoneType type = 2; } repeated PhoneNumber phones = 4; google.protobuf.Timestamp last_updated = 5; } // Our address book file is just one of these. message AddressBook { repeated Person people = 1; } service Test { rpc SayHello (HelloRequest) returns (HelloReply) {} rpc SayHelloAgain (HelloRequest) returns (HelloReply) {} }

MIME types defined: `text/x-protobuf`.