doc: flatten description of 'matching()' predicate to be formatted well current description of 'matching()' revset predicate can't be formatted well on "hg help revset" output. each descriptions for revset predicates (or something like them) are split-ed into lines, and spaces on left side of them are stripped before minirst processing. so, bullet list can't be nested. this patch just flattens description of 'matching()' predicate to be formatted well.