Merge branch 'jt/repo-structure'

"git repo structure", a new command. * jt/repo-structure: builtin/repo: add progress meter for structure stats builtin/repo: add keyvalue and nul format for structure stats builtin/repo: add object counts in structure output builtin/repo: introduce structure subcommand ref-filter: export ref_kind_from_refname() ref-filter: allow NULL filter pattern builtin/repo: rename repo_info() to cmd_repo_info()