Add more types for attr_container, e.g. uint8, uint32, uint64
Add more APIs for attr_container for int8, int16 and int32 types
Rename fields of the union 'jvalue' and refactor some files that use attr_container
Update all links accordingly. Also update links to other repositories
whose branches have renamed.
The references to repositories whose branches have not renamed should be
referencing specific commits anyway, so reference those specific commits
by hash.
