Include warning and error messages

To prevent the user from making mistakes or making clear why something isn't working, include warning and error messages.

For example, when:

An exogenous effect is specified but no covariate information is included
Covariate information is not included in the correct way
An effect is specified for a type of relational event for which it is not defined (e.g., a reciprocity effect is requested but the argument directed is set to false).
An effect is specified that is not defined at all.
An event effect is specified but no event effect information is included.
An inertia weighted/reciprocity weighted effect is requested but no weights are provided.
A both_equal_to effect is requested, but no equal_val is provided.
A riskset is provided but there are actors in the edgelist that are not in the riskset.
Actors are provided but there are actors in the edgelist or riskset that are not in the vector with actors.
Type is set to true but the edgelist doesn't contain event types.

etc.

TilburgNetworkGroup / remstats