Build our own protos

[nrc]

I've copied protos from kvproto so we no longer need that dependency, then we build them ourselves, so we only need the Prost versions. That means we don't need any Git dependencies or need to replace any deps (and can publish the client crates).

Closes #32

PTAL @ekexium

[ekexium]

LGTM.
According to @sticnarf, TiKV is always backward compatible. Thus, we don't have to manually copy any future changes applied to kvproto. But we should clearly state the lowest required version of TiKV server.

[nrc]

According to @sticnarf, TiKV is always backward compatible. Thus, we don't have to manually copy any future changes applied to kvproto.

True, but we will need to copy them if we wish to support new features

But we should clearly state the lowest required version of TiKV server.

Agree