grep: add formatter support Several fields are renamed to be consistent with the annotate command, which doesn't mean the last call for the name unification [1]. Actually, I'd rather rename line_number to linenumber, linenum, lineno or line, but I want to port the grep command to formatter first. [1]: https://www.mercurial-scm.org/wiki/GenericTemplatingPlan#Dictionary I don't have any better name for the list of matched/unmatched texts, so they are just called as "texts".