PARQUET-1125: Add UUID logical type.

LogicalTypes.md

@@ -48,7 +48,18 @@ was converted from an enumerated type in another data model (e.g. Thrift, Avro,
 Applications using a data model lacking a native enum type should interpret `ENUM`
 annotated field as a UTF-8 encoded string. 
 
-The sort order used for `ENUM`s is `UNSIGNED` byte-wise comparison.
+The sort order used for `ENUM` values is unsigned byte-wise comparison.
+
+### UUID
+
+`UUID` annotates a 16-byte fixed-length binary. The value is encoded using
+big-endian, so that `00112233-4455-6677-8899-aabbccddeeff` is encoded as the
+bytes `00 11 22 33 44 55 66 77 88 99 aa bb cc dd ee ff`
+(This example is from [wikipedia's UUID page][wiki-uuid]).
+
+The sort order used for `ENUM` values is unsigned byte-wise comparison.
+
+[wiki-uuid]: https://en.wikipedia.org/wiki/Universally_unique_identifier
 
 ## Numeric Types
 

src/main/thrift/parquet.thrift

@@ -226,6 +226,7 @@ struct Statistics {
 
 /** Empty structs to use as logical type annotations */
 struct StringType {}  // allowed for BINARY, must be encoded with UTF-8
+struct UUIDType {}    // allowed for FIXED[16], must encoded raw UUID bytes
 struct MapType {}     // see LogicalTypes.md
 struct ListType {}    // see LogicalTypes.md
 struct EnumType {}    // allowed for BINARY, must be encoded with UTF-8