Add max_shared flag to expr_cell. Improve app constructor.

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

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

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Fix bug in max_sharing

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Update the build image in README.md
Add format.cpp/.h
Update format.cpp