This change keeps the lumi prefix on our CLI tools.
As @lukehoban pointed out in person, as soon as we do pulumi/coconut#98,
most people (other than compiler authors themselves) won't actually be
typing the commands. And, furthermore, the commands aren't all that bad.
Eventually I assume we'll want something like `lumi-js`, or
`lumi-js-compiler`, so that binaries are discovered dynamically in a way
that is extensible for future languages. We can tackle this during #98.
After a bit more thinking, we will create new SDK packages for each
of the languages we wish to support writing resource providers in.
This is where the RPC goo will live, so I have created a new sdk/
directory, moved the Protobuf/gRPC definitions underneath sdk/proto/,
and put the generated code into sdk/go/ and sdk/js/.
