rustdoc: nodemap doc refreshing
Not pretending to be comprehensive.
- correcting some inconsistencies
- adding a few missing doc-comments
- adding more cross references (in some cases it's right beside
the current documentation item, but it will nevertheless also
be useful, because `rustdoc` will warn us if inconsistencies
arise).
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).