Warn on misformatted annotations (example: --name instead of -- name)

[brunoluiz]

Many times, I forget the space on -- name: XYZ :exec for example. It would be interesting if there was warning in case there is something that is close to the annotation, but not quite. The -- name is the one that I usually get, but I think that might be more cases around the annotation format.

[carpenter-ryan]

I just ran into this and agree this change would be very useful. It's confusing for beginners to understand why code isn't being generated and there are no associated errors or warnings.

[kyleconroy]

Fixed in #859