CtkMenuExpandable: Added an Expandable Menu. Compute correct size
and position with regard to the anchor and the special item inside the menu.

[modified]
  clutk/Makefile.am
  clutk/clutk.h
  clutk/ctk-arb-asm-private.c
  clutk/ctk-arb-asm-private.h
  clutk/ctk-layer-actor.c
  clutk/ctk-main.c
  clutk/ctk-menu.c
  clutk/ctk-menu.h
  data/shaders/Makefile.am
  data/shaders/shaders.h
  gtk-doc.make
  tests/Makefile.am
  tests/test-clutk.c
  vapi/clutk-0.3.gi
  vapi/clutk-0.3.vapi

[added]
  clutk/ctk-menu-expandable.c
  clutk/ctk-menu-expandable.h
  data/shaders/TextureColorMask.fparb
  tests/test-ctk-menu-expandable.c
  tests/test-menu-expandable.c