Setup for New4.
new-bench-integer.hs : Drop New2 from benchmarking.
Check/NewX.hs.tpl : Run encode/decode double tests on New3 and New4.
New4/ : Add second constructor to Natural type.

The Natural type can now represent single Word and multi Word
values separately.
New4/ : Remove SmallPos and SmallNeg constructors from Integer Type.

The Integer type now only has Positive and Negative constructors.