PARQUET-12: Add specs for new logical types.
PARQUET-12: Add specs for new logical types.

This adds the new logical types from #3 to the LogicalTypes.md specification.

Author: Ryan Blue <rblue@cloudera.com>

Closes #5 from rdblue/PARQUET-12-add-new-type-docs and squashes the following commits:

be414fe [Ryan Blue] PARQUET-12: Add specs for new logical types.

rdblue/parquet-format,socialpercon/parquet-format,nvoron23/parquet-format,kostya-sh/parquet-format,nvoron23/parquet-format,winningsix/parquet-format,rdblue/parquet-format,kostya-sh/parquet-format,socialpercon/parquet-format,apache/parquet-format,winningsix/parquet-format,liancheng/parquet-format,nvoron23/parquet-format,liancheng/parquet-format,kostya-sh/parquet-format,apache/parquet-format,winningsix/parquet-format,rdblue/parquet-format,apache/parquet-format,liancheng/parquet-format,socialpercon/parquet-format