Suggest fixes to onError + as usage

[paulpdaniels]

onError looks like onErrorHandle from monix but has a different behavior. However, the signature of onError can make it difficult detect this bug.

Consider:

val e1 = effect.onError(e => log.info("Ok got it $e"))

If e1 is paired with another effect that has an error channel it will unify and it won't be clear to the user that this isn't actually handling the error. However, if this is paired with an operator like as or orElseSucceed, then we can infer that the user either misunderstands onError or could simplify by removing the as since it won't actually do anything.

i.e.

// They either want to use `catch*` or they can just remove the `as`.
val e1 = effect.onError(e => log.info("Ok got it $e") as 42)