Minor fixes in Pull docs

[valencik]

This PR fixes a handful of things in the Pull docs.

In this I noticed that only as has the @tparam and @param annotations, I could add these to the other methods like map and flatMap if that's desired. I'm not sure what the best practice is here.

The docs for fs2 are really great and helpful, thank you so much!

[mpilquist]

Re: @param and @tparam, I don't have strong opinions besides one -- that we don't put a policy in place that results in lots of low quality documentation boilerplate. E.g., if we say "every method should have @param docs for every parameter" and then start writing docs like "@param f The function to apply", we're doing it wrong :)