initial draft of parent_child support
relates to #66 #85 #81 #69
extend header support (ttl/version/timestamp/etc..)

refactor command infrastructure
add internal command templating
improved serialization limiting 'garbage' copies
relates to #66 #85 #81 #69
align Hive writer with new command serialization

relates to #66 #85 #81 #69
add missing class
relates to #66 #85 #81 #69
fix data leak BRC when dealing with Hive data
relates to #66 #85 #81 #69