Add schema descriptor for doc get query string.
Draft query string parsing.

Warn on query string validation errors.
Warn on unknown query options.
Improve query string parsing logic.
Assert on revs_info parameter.
Update user commands.

So that they always use the --id option and -u | --username is only for
authentication credentials
Expose req.edit() function.
Move req decoration functions to module.
Only stash last db call info.

Used by the generic error handler to get arguments for an error
condition.
Update repository URL.