Add Lean default application.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Move test from lean.cpp

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

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

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