Improvements in parsing and printing related to mixed int/real (#1879)

Improvements in parsing and printing related to mixed int/real (#1879)

This eliminates some hacks for dealing with Int/Real.
- Eliminates the use of "to_real" to cast decimals like "2.0" that happen to be Int. We now replace these by (/ 2 1) instead of (to_real 2), which has the advantage of being smt-lib compliant for all theories, including QF_LRA.
- Eliminates the use of a hack to use "type ascriptions" when returning values from a get-value command. Instead, we use division with 1 when necessary.  This affects the output of a few regressions, but we remain smt-lib compliant.
- Addresses a bug with printing arbitrary type ascriptions for smt2 terms. This partially addresses #1852.
- Updates our printing of negative rationals to be (/ (- n) m) instead of (- (/ n m)), which is consistent with the smt lib standard for real values (http://smtlib.cs.uiowa.edu/theories-Reals.shtml).