Implement map using splay_trees

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add support for creating unique internal names.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Implement total order on expressions

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Re-implement rewrite module using rewrite_cell
Fix style-warning
Add Repeat/Success/Fail to rewrite (skeleton)