Breaking changes RE protos

[xd009642]

Since protos are now being compiled into the bindings it might be nice to do some breaking changes and remove a lot of the &[u8] encoded protobuf stuff being passed around and up the minor version number. Alternatively, they can always be side by side for a while but it would be nice to eventually move to just using more "proper" types.

Is there currently a strategy for choosing which protos to add? Or a deprecation policy for how long deprecated items should remain in the code base

[xd009642]

So I've created https://github.com/xd009642/tensorflow-protos-rs what this does is find all the proto files (excluding ones in tf-lite, python, contrib or examples). I then generate the code for them and feature gates! This means that you don't need to pull in everything just what you use.

My thought is that:

1. This makes it easier to add new protos, just a case of enabling a new feature
2. It could potentially become a public part of the API? This could potentially make it easier for people to extend the bindings in their own code. All they need is the tensorflow protos crate and they can enable extra features.

Now for 2. I'm not sure how feasible it is to extend things without exposing them via the bindings as well, but then there are a lot of protos so it might be feasible... @adamcrume if you're not opposed to this I can tidy up the crate some more and work on a PR to add this to tensorflow. I can also add you as a contributor if you'd want as well