Rename TermContext to State

ok. so I took a lighter approach. I only changed the obvious places in the documentation, i.e., those mentioning "term context".

regarding method renames, I only changed those that were talking about `termContext`, not other variants.

there are many places where the State object is still referred by `context`. While not ideal, I think it is not necessarily incorrect -- the State can be considered the context in which something happens. And it is at least better than `TermContext`.

Let's see what Jenkins says, then it may be good to have another pair of eyes check the replacements.