PARQUET-113: Add specs for LIST and MAP annotations.

Draft specs for using `MAP` and `LIST` annotations. This doesn't include a `LIST_ELEMENT` addition to the thrift definition, it is documentation only.

Please help verify that this can read all existing map and list data correctly!
The previous example doesn't follow the recommendation. I'm not sure what the recommendation actually achieves. Could we leave it out and make the specification shorter?