Add lower bound doctests for `saturating_{add,sub}` signed ints
Add lower bound doctests for `saturating_{add,sub}` signed ints

aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust