[gtk] (7 commits) ...Merge branch 'async-highlight' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  4c78f62... gtk-demo: Fontify asynchronously (*)
  ea88795... textbuffer: Some more insert_with_attributes speedup (*)
  aacb06d... gtk-demo: Insert markup incrementally (*)
  80cddd4... gtk-demo: Move the highlighting to a separate file (*)
  a0cdb54... gtk-demo: Fix the Windows build (*)
  bcc5e47... gtk-demo: Do markup parsing incrementally too (*)
  6191404... Merge branch 'async-highlight' into 'master'

(*) This commit already existed in another branch; no separate mail sent