Fiona 0.10

I've tagged 0.10 and uploaded an sdist to PyPI: https://pypi.python.org/pypi/Fiona/0.10.

Changes:

• Add function to get the width of str type properties.

• Handle validation and schema representation of 3D geometry types (#29).

• Return {'geometry': None} in the case of a NULL geometry (#31).

I've also updated the documentation with an explanation in the manual of how "3D" geometries are read and written.