JFP revisions: systematic presentation of key parts of LVish API

[lkuper]

We don't need to show the entire API, but in addition to the series of examples in section 4.2, we should give a systematic presentation of the most important API types and operations that we provide (not necessarily the stuff that data structure implementors would use, but the stuff that application writers would use). Hopefully a lot of this is in the LVish 2.0 Haddocks anyway.

[lkuper]

@rrnewton, do you think you're going to have time in the next couple days to add a ~1-page section that's an overview of the most important LVish API types and operations? We would insert this at the beginning of section 4.2. It could even be a table instead of prose.