PARQUET-322 Document ENUM as a logical type.
PARQUET-322 Document ENUM as a logical type.

Author: Jakub Kukul <jakub@mbr-targeting.com>

Closes #54 from jkukul/master and squashes the following commits:

a2490b2 [Jakub Kukul] PARQUET-322 Document ENUM as a logical type.

apache/parquet-format,apache/parquet-format,apache/parquet-format