Fix #93: Uniform guard parsing

[elbrujohalcon]

Fixes #93 by generating a uniform format for guards.

[elbrujohalcon]

So, after adding these tests, I realized that we can workout in Elvis with what we currently have even if it's more complex.
But building spureous op nodes here to represent stuff that's not really an op, like ; and , would be tricky at best (we might get multiple things wrong, like precedence, line numbers, etc.) and really hard to get it right. For one thing in particular: Guards as a list can represent any number of expressions grouped by ; and any number of expressions grouped by ,. If we want to turn them into ops we need to properly nest them.

[elbrujohalcon]

I'll merge these changes but I #wontfix the Issue.