Coordinates should accept list or tuple

[Taxuspt]

The asserts on lines 30 and 63, i.e.
assert isinstance(coordinates, list)
should also accept tuples, i.e.
assert isinstance(coordinates, (list,tuple))

Since tuples are a valid format on GeoJson and some libraries (e.g. shapely) map shapes to tuples instead of lists.

[connor]

Added in #5 (though not yet merged).