Add more tests. Fix bug in universe implication test.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Use level at kernel expressions

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Remove Prop from kernel

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

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

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add instructions for OS X 10.8 in README.md
Add forall, foldl, foldr to sexpr_funcs
Add more tests on sexpr_funcs
Update format.cpp & format.h
Update test cases - util/format.cpp
Update util/format.cpp & format.h
Fix bug
Add more tests on format
Update format