Update to 1.8.2

• Change MASTER_SITES to GitHub
• Update COMMENT
• Add LICENSE
• Use WRKSRC_SUBDIR
• Update pkg-descr
• Update WWW

Changes: https://github.com/apache/avro/blob/branch-1.8/CHANGES.txt

		https://github.com/apache/avro/commits/branch-1.8/lang/c++