Fully implement encode/decode of all integers and more table elements (clean)

This change is a fuller implementation of what you merged earlier.  It conflicts, but you haven't released that change, so I think you should drop it. This is better done and more comprehensive.

Support packing and unpacking of full range of signed and unsigned integer values,
  though broker differences may make their use problematic.
Fix signedness of integer packing and unpacking (signed were treated as unsigned).
Introduce Net::AMQP::Value::* classes to control packing of table values, with
  all the convenience overloads necessary to make them harmless outside tables.
In tables, pack and unpack values from the "boolean" momdule as AMQP booleans.
In tables, pack and unpack undef as AMQP "void".