This change introduces the scaffolding for a new cmd/cocogo tool,
as part of pulumi/coconut#133. The idea here is to do some very
rudimentary code-gen on a subset of Go, to ease the task of writing
providers. The README describes this in more detail. Eventually
this will presumably expand to being a peer language to CocoPy,
etc., in that real code can be written, but for now it's mostly IDL.
At the moment, the tool really doesn't do anything useful, other
than loading up, parsing, semantically validating, and spewing
some information about the Go packages passed at the command line.
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