Add partial support for metavariables in the normalizer

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add mpq(string s, unsigned radix) constructor
Add SMT frontend (skeletal)
Update smt parser
Update SMT parser
Update
Update options
update
update
Pick get-option, set-option
fix elaborate
checkpoint
Add coercion and elaborator for smt frontend
Update
update
Update
Fix parse_dec()
Update, add tests
Update
update