indicate clearly when there's a yaml parse error

[soenkehahn]

Currently an error gets reported, but it's not always clear that the error comes from trying to parse the yaml file. Example:

error: block sequence entries are not allowed in this context

From this yaml file:

protocol: - foo

It should say something like:

error parsing foo.protocols.yaml: block sequence entries are not allowed in this context

@matthandlersux: I think you mentioned this somewhere, but I can't find it.

[matthandlersux]

i think i mentioned this IRL