Add comments to parser.cpp

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add is_prefix_of for hierarchical names

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add support for pretty printing Dags. Find unused prefix for naming shared expressions.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add support for pretty printing Dags. Find unused prefix for naming shared expressions.