Support Int8 and Int16 as basic type

 Int8 and Int16 are not supported as basic in previos version. Using 4 bytes to store int8 seems not a good idea, which means requiring more storage and read and write very slow. Besides, it is not friendly with regular computing format, such as velox, arrow, vector and so on.

With Int8 and Int16 supported, we can get less storage and better performance on reading and writing. As for forward compatible, we can use version in FileMetaData to choose how to read parquet data.