added failing NaN test for agrad/rev/trunc
fixed agrad/rev/trunc so NaN test passes
added failing NaN test for agrad/rev/round
fixed agrad/rev/round to return gradient NaN for input NaN
Merge branch 'feature/issue-845-round-nan' into feature/issue-847-fwd-functions-nan
Merge branch 'feature/issue-845-trunc-nan' into feature/issue-847-fwd-functions-nan