cpp/python: export documented functions to construct sets from isl_aff

cpp/python: export documented functions to construct sets from isl_aff

The following documented operations are exported:

	isl_aff_eq_set
	isl_aff_ne_set
	isl_aff_le_set
	isl_aff_lt_set
	isl_aff_ge_set
	isl_aff_gt_set

The function variants that produce basic sets are not yet exported, as
it is unclear if there are common use cases for them.

Signed-off-by: Tobias Grosser <tobias@grosser.es>
Reviewed-by: Nicolas Vasilache <nicolas.vasilache@gmail.com>
Reviewed-by: Oleksandr Zinenko <oleksandr.zinenko@inria.fr>
Signed-off-by: Sven Verdoolaege <sven.verdoolaege@gmail.com>