Fix bug in pretty printer

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Move '\' character to class b

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Rename builtin operator if-then-else

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Improve parser

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>