Produce better error messages

this discussion is a fork from #79 .

@caolan said

> we should probably make that a nicer error message! (pull requests welcome for that)

@greelgorke said:

> attempt is to check for the value being a highland stream (or feature-detect, but it's less reliable in our case) and to produce an error if it doesn't pass the check (instead of throwing)

@caolan also said:

> We currently don't wrap iterator (eg, map, filter...) calls with try/catch in order to pass those sync errors down the pipeline but we probably should!

No file or test is named. Start by tracing the stream-value check and iterator calls such as map and filter discussed here, then clarify the intended error behavior with the maintainers. Done should mean that the agreed invalid-value and synchronous-error cases produce the specified messages or flow down the pipeline without being thrown.

Written by the indexing model from the issue text.