Add blockData Enums

Add enums defining variant of block
For example the colour of a wool block or the direction stairs point
Use back ported IntEnum as allows direct integer comparison
Available in 2.7, 3.2 and 3.4
  https://pypi.python.org/pypi/enum34
  https://docs.python.org/3/library/enum.html#intenum
Make this a docstring please.