Comment cleanups to improve generated docs

- added comments to fields which didn't have any.
- changed all `//` comments to the new format
- fixed indents/line lengths/style on lines I touched
Did you want to make this change? Having this field nullable may be preferable --> e.g., null would mean return all variants. Then again, 0 can encode that just as well... In the schema, we should probably document how to get this request to return an unlimited number of variants.