feat(go): add a Go guest generator (WIP, do not merge!)

[Mossaka]

I started this work as a hackathon project. It currently can only work with integer functions for both import/export. It's not nearly half done yet, but I want to put this out to those who are interested in. Any feedback on the go user application's experience would be much welcomed!

This is also a place to track things to be done:

• [ ] type record
• [ ] type flags
• [ ] type tuple
• [ ] type varient
• [ ] type option
• [ ] type union
• [ ] type enum
• [ ] type resource
• [ ] type alias
• [ ] type list
• [ ] type builtin
• [ ] "go:generate" and executable that hides "init" function

Signed-off-by: Jiaxiao Zhou [email protected]