Lint protobuf files, place in xviz.v2 package, ensure bazel compat

We are using Uber's prototool 1.7 for lint with the provided
prototool.yaml setting which rules we are not following. These are not
being followed so that JSON emitted and consumed by the protobuf types
matches that in the JSON schema.

Bazel compatibility allows other projects to pull in our source
releases and use the protobuf rules directly.

See the `docs/protocol-formats/protobuf-protocol.md` for more details
on Bazel and lint/formatting.

docs/protocol-formats/protobuf-protocol.md

@@ -0,0 +1,62 @@
+# XVIZ Protobuf Protocol Format
+
+The XVIZ JSON schema is compatible with a set of protobuf files found in the `xviz/v2` folder of the
+XVIZ repository. With these files you can produce JSON data that is compatible with the XVIZ JSON
+schema and XVIZ clients.
+
+## Current Status
+
+**UNSTABLE** - the Prototuf schema for XVIZ is under active development. Anything can change in an
+unversioned way: file structure, type names, or naming style to name just a few.
+
+## Linting & Formatting Protobuf
+
+We are using Uber's [prototool](https://github.com/uber/prototool) (version 1.7) to keep our files
+consistent and following common conventions where possible (see `prototool.yaml` in the root for
+exceptions):
+
+To lint the files:
+
+    prototool lint ./xviz/v2
+
+To format the files:
+
+    prototool format -w ./xviz/v2
+
+## Using with Bazel
+
+First you would use an external repository rule in your `WORKSPACE` like this but with the **proper
+version** (newer than `1.0.0-beta14`) and matching sha256 sum.
+
+```
+http_archive(
+    name = "com_github_uber_xviz",
+    build_file = "//third_party:xviz.BUILD",
+    sha256 = "5dee4a6d73b9032e589868fa67748ad2be3cc7face147c192f569c54170ef07c",
+    strip_prefix = "xviz-1.0.0-beta.14",
+    urls = ["https://github.com/uber/xviz/archive/v1.0.0-beta.14.zip"],
+)
+```
+
+The above rule references this `xviz.BUILD` file. This one generate C++ but you can modify it to
+produce other language specific Protobuf bindings.
+
+```
+proto_library(
+    name = "proto",
+    srcs = glob(["xviz/v2/*.proto"]),
+    deps = [
+        "@com_google_protobuf//:descriptor_proto",
+        "@com_google_protobuf//:struct_proto",
+    ],
+)
+
+cc_proto_library(
+    name = "cc_proto",
+    visibility = ["//visibility:public"],
+    deps = ["proto"],
+)
+```
+
+You would reference this rule in your other Bazel by using the following target:
+`@com_github_uber_xviz//:cc_proto`

docs/protocol-schema/introduction.md

@@ -73,3 +73,5 @@ types described below:
   types into JSON
 - [Binary protocol](/docs/protocol-formats/binary-protocol.md) - a Hybrid JSON binary protocol
   designed for larger data sets and faster performance
+- [Protobuf protocol](/docs/protocol-formats/protobuf-protocol.md) - an in development Protobuf
+  schema that is compatible with the JSON protocol

modules/schema/package.json

@@ -24,7 +24,7 @@
   },
   "scripts": {
     "build-schema": "node ./build-schema",
-    "build-protos": "pbjs --keep-case --target json --path ./proto/v2/*.proto --out dist/proto.v2.json",
+    "build-protos": "pbjs --keep-case --target json --proto-path ../.. --out dist/proto.v2.json ../../xviz/v2/*.proto",
     "pre-build": "npm run build-schema && npm run build-protos"
   }
 }