tidy eval terms and functions <--> base R terms and functions

[jennybc]

As discussed in meeting, anything you can do to help people do these lookups and reverse lookups would be awesome. Some information is already sprinkled in rlang help files, but it's still hard to find and it's not always there.

For the most part, tidy eval terms are named with more discipline re: doing/being what they say. But because base R's names are often idiosyncratic/confusing, this complicates mapping from one to the other (think about substitute(), "expressions" or "frames"), so an explicit mapping by an expert is helpful. Basically, demarcate those hazardous bits with bright yellow caution tape.

This is related to issue #1 re glossary and maybe they can somehow be addressed at the same time.