Merge branch 'maint' of git://linux-nfs.org/~bfields/git into maint

* 'maint' of git://linux-nfs.org/~bfields/git:
  core-tutorial: minor cleanup
  documentation: replace Discussion section by link to user-manual chapter
  user-manual: todo updates and cleanup
  user-manual: fix introduction to packfiles
  user-manual: move packfile and dangling object discussion
  user-manual: rewrite object database discussion
  user-manual: reorder commit, blob, tree discussion
  user-manual: rewrite index discussion
  user-manual: create new "low-level git operations" chapter
  user-manual: rename "git internals" to "git concepts"
  user-manual: move object format details to hacking-git chapter
  user-manual: adjust section levels in "git internals"