Merge CmpNat and CmpSymbol in 7.8

Hi, based on requests from a couple of people I added a couple of type-level functions for type nats and type symbols. Could we get these merged in 7.8? The relevant commits are: In GHC: 5e4bdb5fc5e741522cbb787731422da3f12aa398 Implement ordering comparisons for type-level naturals and symbols. In base: 5edb063688e73ec00fd1f61ac0e8317dd122f44a Comments only. c1d3546420ee482bbbd9f15d45a6e8a26304d419 Add functions for comparing type-level Nats and Symbols. Thanks! -Iavor