Example data to test implementations

[cholmes]

One idea that @jorisvandenbossche suggested is that we should have a set of data that shows the range of the specification, that implementors can use to make sure they're handling right, and which could be the basis of 'integration' testing.

This would include geoparquet files that have a variety of projections, geometry types (including multiple geometry types as in #119), plus things like multiple geometry columns, different edges values, etc. It could also be good to have a set of 'bad' files that can also be tested against.

[cholmes]

There was also work on this in #204 for the new geometry encodings. We should figure out if we want to try to do more for 1.1

[jorisvandenbossche]

If I can finish #134, then I think we can close this issue with that PR