Initial tests coverage for golang jenny

[K-Phoen]

Similar to #13, but for Go.

Things to notice:

• I run the compiler passes for Go before running the raw types jenny. This is because the IR supports some concepts that don't translate directly into Go (disjunctions, in particular).
• the Go output isn't properly formatted: it's expected, that's the job of a post-processor
• disjunctions aren't properly handled. In their current form, most of them can't properly be marshaled to/unmarshaled from JSON. It's a leftover from the PoC days and since it's not trivial to fix/finish, it will be done in another PR and is tracked by a different issue.
• there are some places in the code that should never be reached ©, but no error would bubble up if we reached them. The error handling should definitely be improved in another PR (see Improve Go RawTypes jenny error handling #18).

Related to #6

[spinillos]

Looks like fine.