* add signature information when help on one command
* tell user that one command support operated on cell paths
Also, make type output to be more friendly, like `record<>` should just be `record`
And the same to `table<>`, which should be `table`
* simplify code
* don't show signatures for parser keyword
* update comment
* output arg syntax shape as type, so it's the same as describe command
* fix string when no positional args
* update signature body
* update
* add help signature test
* fix arg output format for composed data type like list or record
* fix clippy
* add comment
* update docs to refer to length instead of count
* rename count to length
* change all occurrences of 'count' to 'length' in tests
* format length command
* fix case where parent_name was {nu, term} and possibly others in the future by doing an extra test first to see if if the *parent_name key actually exists in cmap
* update with help generate_docs testing
