1. add simplifications for   a. nested superpose   b. if with undefined (first) branch 2. infer types for Measures, not just values 3. widen the cases where normal density is recognized
1. add simplifications for
  a. nested superpose
  b. if with undefined (first) branch
2. infer types for Measures, not just values
3. widen the cases where normal density is recognized

zachsully/hakaru,zaxtax/hakaru,suhailshergill/hakaru,bitemyapp/hakaru,zaxtax/hakaru,zachsully/hakaru