Add CLI

[aluttik]

There's currently some scripts in the cmd/ directory you can call like:

go run cmd/parse/main.go path/to/nginx.conf > nginx.conf.json
go run cmd/build/main.go path/to/nginx.conf.json > nginx.conf

But they're not nearly as useful as the python crossplane CLI.

[andrerfcsantos]

Hey,

I would like to help in this issue.

My idea is to make this a single binary with parse and build being subcommands of that binary, as is the case of the python cli. This would also make way to add future commands (which I also can help).

I'm thinking of using cobra to make the cli.