fix(library/rewriter): unused variable warnings
feat(util/list): filter template

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(util/list): map_append template

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(util/name_set): add mk_unique (with respect to a name_set)

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/tactic): add focus tactical

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