We are renaming Lumi to Pulumi Fabric. This change simply renames the
pulumi/lumi repo to pulumi/pulumi-fabric, without the CLI tools and other
changes that will follow soon afterwards.
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.
