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 mapType method in ConversionPatterns [validates the "value" name](https://github.com/apache/incubator-parquet-mr/blob/master/parquet-column/src/main/java/parquet/schema/ConversionPatterns.java#L70), although I'm not sure why. We don't really need these, but having them answers two questions that everyone will have when implementing. First, what do I name those fields? And the second follow-up, do they always have to be named that way?