Expose environment API in the frontend object. Add support for formatting objects.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Fix crash when trying to format an object created by a different frontend.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Improve formatter usage. Fix bug in object printer.

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

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Make sure formatter can be used even when associated frontend is not in scope.

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

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

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

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