Merge branch 'jh/notes' (early part)

Merge branch 'jh/notes' (early part)

* 'jh/notes' (early part):
  Add selftests verifying concatenation of multiple notes for the same commit
  Refactor notes code to concatenate multiple notes annotating the same object
  Add selftests verifying that we can parse notes trees with various fanouts
  Teach the notes lookup code to parse notes trees with various fanout schemes
  Teach notes code to free its internal data structures on request
  Add '%N'-format for pretty-printing commit notes
  Add flags to get_commit_notes() to control the format of the note string
  t3302-notes-index-expensive: Speed up create_repo()
  fast-import: Add support for importing commit notes
  Teach "-m <msg>" and "-F <file>" to "git notes edit"
  Add an expensive test for git-notes
  Speed up git notes lookup
  Add a script to edit/inspect notes
  Introduce commit notes

Conflicts:
	.gitignore
	Documentation/pretty-formats.txt
	pretty.c